CHEMICAL   LECTURE   EXPERIMENTS 


-y'^y^ 


CHEMICAL    LECTURE 
EXPERIMENTS 


BY 


FRANCIS   GANO   BENEDICT,  Ph.D. 

INSTRUCTOR    IN    CHEMISTRY    IN    WESLEYAN    UNIVERSITY 


Neto  gork 
THE   MACMILLAN   COMPANY 

LONDON:  MACMILLAN  &  CO.,  Ltd. 
1909 

All  rights  reserved 


^)M 


Copyright,  1901, 
By  the   MACMILLAN  COMPANY. 


Set  up  and  electrotyped.    Published  May,  igoi.     Reprinted 
July,  1909. 


^J^**«  * 


J.  S.  Cushlng  Co.  —  Heiwick  &  Smith  Co, 
Norwood,  Mass.,  U.S.A. 


a   r   ^ 


Eo  tje  Plemorg  of 
JOSIAH   PAESO:^^S   COOKE 

FOR   FORTY-THREE    YEARS   ERVING    PROFESSOR   OF    CHEMISTRY 
AND    MINERALOGY    IN    HARVARD    UNIVERSITY 

THIS  BOOK  IS  DEDICATED 

AS    A    TRIBUTE    TO   AN    INSPIRING    TEACHER 

THE  A  UTHOR 


Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

IVIicrosoft  Corporation 


http://www.archive.org/details/chemicallectureeOObenerich 


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PREFACE 


IBcture  Z' 


The  demonstration  of  chemical  phenomena  o: 
table,  though  originally  strongly  imbued  with 
of  mysticism  inherited  from  the  hermetic  art,  has  always 
been  considered  an  essential  phase  of  chemical  instruction. 
After  chemistry  was  placed  on  a  broader  basis  by  Lavoisier, 
and  the  black  art  converted  to  a  science,  experimental  lec- 
tures still  remained  a  legitimate  factor  in  presenting  the 
subject.  Soon  text-books  and  class  recitations  and  later 
laboratory  exercises  for  the  student  supplemented  the  lec- 
ture, and  with  the  introduction  of  the  latter  a  tendency  to 
neglect  the  experimental  lecture  developed.  Laboratory 
exercises,  however  great  their  influence  in  developing  the 
experimental  side  of  teaching  the  science,  have  their  limita- 
tions, experimentally  and  educationally,  and  cannot  sup- 
plant the  experimental  lecture,  for  it  is  in  the  lecture, 
and  there  only,  where  each  experiment  stands  out  clearly 
defined  and  unattended  by  the  distractions  necessarily 
accompanying  laboratory  exercises,  that  the  first  accurate 
observations  of  chemical  phenomena  can  be  made  by 
students. 

The  late  Professor  Josiah  P.  Cooke,  though  one  of  the  first 
to  introduce  laboratory  exercises  into  the  educational  insti- 
tutions of  this  country,  said,  nevertheless,  "Experimental 
lectures  are,  I  am  convinced,  much  the  best  way  of  pre- 
senting these  subjects  [Chemistry  and  Physics]  as  syste- 
matic portions  of  knowledge."  His  belief  in  the  method 
gave   rise   to   that   grand  series  of   experimental    lectures 


Vm  PREFACE 

delivered  for  more  than  forty  years  at  Harvard  College; 
a  course  of  lectures  whose  stimulus  to  chemical  study  and 
research  has  influenced  so  many  of  the  prominent  teachers 
of  chemistry  in  this  country. 

The  most  versatile  and  fluent  chemical  lecturer  of  his 
day,  the  late  Professor  Victor  Meyer,  was  another  great 
advocate  of  the  experimental  lecture.  The  breadth  and 
scope  of  his  lectures  gave  unusual  opportunities  for  experi- 
ments, and  his  contributions  to  experimental  science  were 
of  so  brilliant  and  striking  a  character  as  to  infuse  new  life 
into  the  chemistry  of  the  lecture  room. 

Constant  attendance  on  Professor  Cooke's  lectures  for 
five  successive  years  gave  the  first  impulse  to  the  preparar 
tion  of  this  book,  an  impulse  which  was,  through  my  inter- 
course with  Professor  Meyer,  stimulated  into  a  purpose. 

The  object  of  this  book  is  primarily  to  furnish  teachers 
with  a  large  number  of  reliable  lecture  experiments.  That 
these  experiments  require  in  many  cases  different  treat- 
ment from  those  performed  in  the  laboratory  will  be  obvi- 
ous when  it  is  considered  that  the  demonstrations  on  a 
lecture  table  must  be  of  sufficient  magnitude  and  of  a 
character  marked  enough  to  enable  the  phenomena  to  be 
observed  at  as  great  a  distance  as  possible. 

The  two  or  three  previous  works  treating  of  this  branch 
of  experimental  science  are  remarkably  complete  and  ex- 
haustive, but  there  is  one  serious  hindrance  to  their  ready 
adoption  in  most  colleges  and  schools,  i.e.,  the  requirement 
of  elaborate  and  costly  apparatus  and  the  assumption  of 
great  proficiency  on  the  part  of  the  teacher  in  glass-blowing 
and  general  manipulation.  To  overcome  this  difficulty  all 
experiments  requiring  especially  elaborate  apparatus  have 
here  been  rigorously  excluded.  By  adhering  to  this  rule 
some  familiar  experiments  have  doubtless  been  omitted, 
but  it  has  been  possible  in  many  cases  to  substitute  an 


PREFACE  IX 

equivalent  experiment.  As  most  of  the  apparatus  required 
is  that  commonly  used  by  students,  it  is  considered  that 
the  large  majority  of  experiments  here  presented  may  be 
easily  performed  with  an  ordinary  laboratory  equipment. 

As  an  aid  to  the  inexperienced  the  descriptions  of  the 
apparatus  and  the  manipulations  are  given  in  considerable 
detail  together  with  many  suggestions  regarding  the  prepa- 
ration and  care  of  apparatus.  Experimental  manipulation 
is  not,  however,  merely  a  matter  of  rules,  and,  while  the 
euggestions  given  will,  it  is  hoped,  prove  of  value  to  the 
inexpert,  the  fullest  confidence  so  essential  to  successful 
experimenting  must  be  obtained  by  experience. 

With  but  few  exceptions  the  elements  are  treated  in  the 
order  of  their  arrangement  in  the  periodic  classification. 
An  attempt  has  been  made  to  have  the  cross-references  in 
the  index  so  complete  that  a  list  of  experiments  on  any 
subject  may  be  readily  obtained. 

The  material  here  presented  has  been  prepared  with 
reference  also  to  its  use  by  students  desiring  collateral 
reading  in  connection  with  experimental  lectures.  As  an 
elaboration  of  the  laboratory  manual,  the  book  may  also  be 
used  by  students  for  the  preparation  of  many  compounds 
not  considered  in  elementary  text-books. 

The  great  number  of  contributors  to  the  evolution  of  the 
phase  of  experimental  chemistry  treated  in  this  book  ren- 
ders it  impossible  to  designate  with  any  degree  of  justice 
the  originators  of  the  very  large  majority  of  experiments 
of  this  class,  and  rather  than  encumber  the  book  with  mul- 
titudinous references  I  prefer  personally  to  make  no  espe- 
cial claim  to  originality.  My  indebtedness  to  the  former 
works  pertaining  to  this  subject,  all  of  which  have  been 
freely  drawn  upon,  is  inadequately  expressed  by  enumera- 
tion in  the  list  on  p.  419. 

In  performing  the  experiments,  which  have  all  had  my 


X  PREFACE 

personal  supervision,  I  have  enjoyed  the  skilful  assistance 
of  Drs.  H.  M.  Smith  and  J.  F.  Snell  and  Mr.  W.  S.  Baker. 
I  am  deeply  indebted  to  Professor  W.  P.  Bradley,  who  has 
rendered  me  signal  service  in  the  many  suggestions  born  of 
his  long  experience  in  chemical  manipulation.  I  would 
also  express  my  thanks  to  Professor  W.  0.  Atwater,  who 
generously  placed  his  magnificent  chemical  library  at  my 
disposal.  The  index  was  prepared  by  Mrs.  Cornelia  Golay 
Benedict,  whose  assistance  in  this  and  in  many  other  ways 
has  made  the  writing  of  this  book  possible. 

The  object  of  this  book  will  have  been  attained  if  it  sup- 
plements to  some  extent  the  admirable  works  of  Arendt, 
Heumann,  and  Newth  in  their  task  of  stimulating  the 
demonstration  of  chemical  phenomena. 

F.  G.  B. 

Wesletan  University, 
middletown,  connecticut. 


TABLE   OF   CONTENTS 

PAGE 

Introduction 1 

Oxygen          ...........  8 

Ozone 31 

Hydrogen    ...........  39 

OXYHYDROGEN    GaS    AND    WaTEK 62 

Hydrogen  Peroxide  .........  74 

Chlorine 80 

Hydrochloric  Acid    •. 89 

Chlorine  Monoxide 98 

Hypochlorous  Acid 99 

Chlorine  Peroxide 101 

Chloric  Acid 104 

Perchloric  Acid 104 

Bromine 106 

Hydrobromic  Acid 108 

Iodine 112 

Hydriodic  Acid 117 

Iodic  Acid 124 

Hydrofluoric  Acid 127 

Sulphur 130 

Hydrogen  Sulphide 135 

Hydrogen  Persulphide 147 

Sulphur  Monochloride      ........  148 

Sulphur  Dioxide  and  Sulphurous  AciU          ....  149 

Hydrosulphurous  Acid 157 

xi 


Xll  TABLE   OF   CONTENTS 

PAOB 

Sulphur  Trioxide .        .        .  158 

Sulphuric  Acid 164 

Selenium 177 

Nitrogen 180 

Atmospheric  Air 186 

Ammonia 189 

Nitrogen  Chloride 204 

Nitrogen  Iodide 205 

Hydroxylamine .         .  207 

Nitrous  Oxide 208 

Nitric  Oxide 211 

Nitrous  Anhydride  and  Nitrous  Acid 218 

Nitrogen  Peroxide 219 

Nitric  Acid 222 

Hydrazine    ...........  228 

Hydrazoic  Acid 229 

Phosphorus 232 

Hydrogen  Phosphide           ........  249 

Phosphonium  Iodide   .........  258 

Phosphorus  Trichloride 259 

Phosphorus  Pentachloride 261 

Phosphorus  Bromides .  263 

Phosphorous  Acid 264 

Hypophosphorous  Acid 266 

Phosphorus  Pentoxide  and  Phosphoric  Acids        .        .         .  266 

Arsenic 268 

Antimony 273 

Boron 278 

Silicon 283 

Carbon 291 

Carbon  Monoxide 296 

Carbon  Dioxide 303 

Carbon  Bisulphide 317 


TABLE   OF   CONTENTS  Xlll 

PAGK 

Methane 319 

Ethylene 320 

Acetylene 323 

Illuminating  Gas 324 

Structure  of  Flame 328 

Reciprocal  Combustion     .         .         .         .         .         .         .         .  339 

Sodium 349 

Potassium 354 

Ammonium  Compounds         .         .         .         .         .         .         .         .  368 

Calcium 363 

Strontium  and  Barium 367 

Magnesium 371 

Zinc  and  Cadmium 377 

Mercury 381 

Copper 384 

Silver 388 

Aluminium 391 

Tin 396 

Lead 400 

Bismuth 404 

Chromium 405 

Iron 409 

Cobalt  and  Nickel 413 

Appendix .         .         .  419 

Index 423 


CHEMICAL  LECTURE  EXPERIMENTS 


INTRODUCTION 

Owing  to  the  independent  nature  of  each  experiment  the 
description  is  in  most  instances  prefaced  with  a  short  state- 
ment of  the  nature  of  the  reaction  under  consideration. 
The  equations  have  been  given  as  far  as  practicable,  and 
where  the  reaction  is  not  regular  and  the  product  is  of  a 
complex  nature,  the  fact  that  the  equation  represents  the 
general  reaction  only  is  indicated  by  its  being  followed  by 
an  interrogation  mark  enclosed  in  brackets. 

To  facilitate  the  preparation  of  experiments,  a  list  of  the 
apparatus  and  the  chemicals  required  has  been  appended  to 
experiments  demanding  anything  not  ordinarily  found  on  a 
lecture  table.  Just  how  extensive  such  a  list  should  be  has 
been  a  matter  of  considerable  question,  and  to  avoid  undue 
repetition  it  is  assumed  that  burners,  test-tubes,  retort 
stands,  pneumatic  trough,  and  such  general  apparatus,  as 
well  as  the  common  reagents,  are  either  on  the  lecture  table 
or  within  reach. 

Where  approximate  quantities  of  solid  substances  are 
required,  it  has  been  the  custom  hitherto  to  make  reference 
to  the  size  of  a  "pea,"  "walnut,"  "'hazelnut,"  "egg,^'  and 
so  forth.  The  latitude  thereby  allowed  in  the  selection  of 
the  quantity  of  material  is  often  much  greater  than  that 
intended  by  the  writer,  owing  to  the  variations  in  the  con- 
ceptions of  the  different  sizes  by  individual  experimenters. 
Believing    that    this    phraseology    is    unsatisfactory,    the 

B  1 


Z  CHKMICAL   LECTITJIB   EXPERIMENTS 

approximate  diameter  of  an  equivalent  spherical  mass  is 
here  used.  A  "  7  mm.  piece  "  of  sodium  would  mean  a  mass 
whose  general  form  if  spherical  would  have  an  approximate 
diameter  of  7  mm.  As  a  matter  of  fact  a  piece  of  this 
dimension  would  ordinarily  be  designated  as  being  the 
"size  of  a  pea."  A  paper  millimeter  scale  pasted  to  the 
table  or  wall  will  materially  aid  in  estimating  the  various 
sizes. 

Under  the  various  subjoined  heads  suggestions  are  made 
regarding  the  general  apparatus  required. 

Weights  and  measures.  —  The  metric  system  of  weights 
and  measures  alone  is  used.  A  meter  stick  and  some  cheap 
scales  with  a  set  of  metric  weights  should  be  at  hand. 
Sheets  of  paper  of  convenient  size  to  place  on  the  scale 
pans  should  be  cut  ready  for  use  in  weighing  out  solids. 
Corrosive  solids  should  be  weighed  in  previously  tared  watch- 
glasses.  Liquids  are  best  measured  in  the  several  sizes  of 
graduated  cylinders. 

Glassware.  —  All  glassware  except  test-tubes  should  be 
made  of  Jena  glass.  The  use  of  this  glassware  is  deemed 
of  such  importance  that  it  is  especially  emphasized  in  the 
descriptions  of  many  experiments.  By  thus  including  it  in 
the  specifications  of  apparatus,  it  must  not  be  thought  that 
other  forms  of  glass  will  not  serve  the  purpose,  though  the 
advantage  always  lies  with  the  apparatus  constructed  with 
Jena  glass. 

It  will  be  observed  that  all  glassware  required  is  of  the 
nature  ordinarily  used  in  the  laboratory.  The  Erlenmeyer 
form  of  flask  is  especially  recommended,  and  in  general  is 
to  be  substituted  for  the  older  form,  as  it  is  much  easier  to 
clean,  and  the  greater  area  of  the  bottom  renders  it  more 
stable  and  results  in  a  more  even  distribution  of  heat. 
Bulb-tubes  are   especially  advantageous,  but  may  in  most 


INTRODUCTION  3 

cases  be  replaced  by  short  pieces  of  combustion-tube,  though 
in  this  case  if  the  substance  to  be  acted  upon  is  a  liquid  or 
an  easily  melted  solid,  it  should  be  placed  in  a  porcelain 
boat. 

Test-tubes  and  ignition-tubes.  —  A  rack  should  be  filled 
with  clean,  dry  test-tubes  of  different  sizes,  and  an  assort- 
ment of  hard-glass  test-tubes  or  ignition-tubes  should  be 
provided.  A  plate  containing  clean  white  sand  is  useful  to 
lay  ignition-tubes  on,  and  to  place  under  heated  tubes  to 
catch  anything  that  might  fall. 

Kipp  gas  generators.  —  Though  faulty  in  principle,  the 
Kipp  generator,  or  one  of  its  various  modifications,  remains 
to-day  the  only  portable  gas  generator  for  the  lecture  table. 
At  least  two  generators  are  necessary,  —  one  for  hydrogen, 
and  the  other  for  carbon  dioxide.  A  large  quantity  of  dilute 
hydrochloric  acid  (1 : 1)  should  be  made  up  ready  for  use  in 
these  generators.  As  a  rule,  the  simpler  and  less  expensive 
the  form  of  Kipp  used,  the  better.  A  tubulature  in  the  lower 
chamber  is  desirable.  Especial  care  should  be  exercised  to 
have  all  joints  and  connections  tight. 

Batteries. — An  open  circuit  battery,  preferably  of  the 
"dry''  form,  and  a  "bichromate"  battery  of  six  cells  are 
necessary.  The  expensive  windlass  form  of  bichromate 
battery  may  be  replaced  by  simpler  though  less  convenient 
forms  at  a  much  lower  cost.  The  zincs  should  be  amalga- 
mated     An  excellent  battery  solution  is  made  as  follows :  — 

600  g.  potassium  dichromate. 
1000  cc.  concentrated  sulphuric  acid. 
4800  cc.  water. 

Splinters,  tapers,  and  candles.  —  Splinters  of  wood  are  used 
frequently  in  testing  for  oxygen,  and  should  accordingly  be 
of  a  material  that  will  retain  a  spark  for  some  time.     The 


4  CHEMICAL   LECTURE   EXPERIMENTS 

best  splinters  for  this  purpose  are  made  from  cigar-box 
wood.  A  supply  should  always  be  kept  in  a  place  where 
they  cannot  become  wet.  An  assortment  of  candles  con- 
sisting of  short  pieces  of  the  ordinary  household  size,  and 
especially  the  small  candles  so  often  used  for  decorative 
purposes,  should  be  at  hand.  The  latter  will  be  found 
particularly  convenient,  as  they  can  be  readily  thrust  into  a 
small-necked  vessel.  Suitable  wires  and  supports  for  low- 
ering the  candles  into  a  vessel  or  thrusting  them  up  into  an 
inverted  jar  are  desirable. 

Asbestos  paper.  —  The  free  use  of  this  paper,  which  should 
be  about  the  thickness  of  ordinary  blotting-paper,  is  espe- 
cially recommended.  As  a  protection  to  the  table,  as  a  heat 
distributor  under  a  flask  or  beaker  to  be  heated,  and  as  a 
valuable  accessory  in  many  experiments,  it  is  almost  indis- 
pensable on  the  lecture  table. 

Compressed  gases.  —  Cylinders  of  compressed  or  liquefied 
gases,  if  not  of  an  unwieldy  size,  are  an  invaluable  adjunct 
to  a  lecture  table.  Their  high  price  prohibits  their  ever 
being  universally  used,  but  cylinders  of  liquefied  carbon 
dioxide  are  found  in  many  drug  stores  and  confectionery 
shops.  Liquefied  nitrous  oxide  is  used  by  many  dentists, 
and  may  be  borrowed,  the  gas  used  being  determined  by  the 
loss  in  weight.  Liquefied  anhydrous  ammonia  is  an  essen- 
tial in  most  refrigerating  plants  where  a  partially  filled 
cylinder  may  often  be  borrowed.  Compressed  oxygen  is  of 
such  importance  that  it  has  received  special  treatment  in 
the  text.  All  of  these  gases,  together  with  hydrogen  and 
sulphur  dioxide,  may  be  obtained  in  compressed  or  liquefied 
form  from  the  regular  dealers  in  chemical  supplies.  Where 
it  is  possible  to  obtain  them  near,  home,  however,  the  ex- 
pense of  the  express  or  freight,  as  well  as  rental  on  the 
cylinders,  is  saved. 


INTRODUCTION  6 

Shields,  gauntlets,  and  eyeglasses.  —  Experiments  of  a 
dangerously  explosive  nature  are  not  to  be  recommended  to 
the  inexperienced.  It  is  true,  however,  that  experiments 
with  explosive  mixtures  can  be  made  on  a  small  scale  with 
practically  no  danger  to  experimenter  or  observers,  by 
using  small  quantities  of  material  and  placing  the  apparatus 
between  glass  screens.  In  this  way  all  flying  particles  of 
glass  or  chemicals  are  confined  to  the  area  between  the 
shields,  and  no  harm  can  possibly  come.  The  simplest 
screen  is  represented  in  Fig.  50,  p.  102,  and  can  be  cheaply 
constructed  by  any  carpenter.  Two  such  screens  will  serve 
as  a  protection  in  nearly  all  experiments,  though  in  a 
few  cases  four  may  be  used  to  advantage.  One  screen  is 
placed  between  the  apparatus  and  the  audience,  and  the 
other  between  the  experimenter  and  the  apparatus.  This 
leaves  two  danger  zones  lengthwise  of  the  table,  but  if  no 
inflammable  materials  are  carelessly  exposed  on  the  table, 
no  danger  need  be  feared. 

For  many  experiments  a  protection  to  the  hand  is  indis- 
pensable. The  driving  glove  or  gauntlet  (Fig.  7,  p.  19)  is 
especially  well  adapted  to  this  work,  as  the  coat  sleeve  may 
be  thrust  into  the  sleeve  of  the  gauntlet,  and  thereby  the 
possibility  of  bits  flying  up  the  open  sleeve  may  be  avoided. 

In  experiments  where  there  is  an  evolution  of  intense 
light  it  is  advisable  to  cover  the  eyes  with  colored  glasses. 
Glasses  of  smoked  or  colored  mica  are  furthermore  useful 
as  a  protection  in  many  operations  of  an  explosive  nature. 
With  proper  use  of  the  glass  screens,  however,  protection 
to  the  eyes  except  from  the  effect  of  bright  light  is  seldom 
necessary. 

Reagents  and  test  papers.  —  A  full  set  of  the  common 
qualitative  reagents,  together  with  the  various  test  papers, 
such  as  red  and  blue  litmus,  turmeric  and  iodo-starch,  as 
well  as  touch-paper,  should  be  provided. 


6 


CHEMICAL  LECTUBE  EXPERIMENTS 


Precipitations  may  be  made  in  glass  cylinders  or  conical 
wine-glasses.  If  the  precipitation  is  to  be  made  in  a  hot 
solution,  the  test-tube  on  foot  (Fig.  51,  p.  103),  made  of 
thin  glass  which  will  stand  heat,  is  the  vessel  best  adapted. 
A  supply  of  long  and  short  glass  rods  whose  ends  have 
been  rounded  in  the  flame  should  be  provided. 


Aspirators,  water  pumps,  and  water  blast. — The  sim- 
plest form  of  aspirator  is  made  by  fitting  a  two-holed  cork 
to  a  large  bottle  and  inserting  in  one  hole  a  glass  tube  ex- 
tending to  the  bottom  of  the  bottle,  while  a  glass  elbow  is 
thrust  into  the  second  hole  in  the  cork.  By  attaching  a 
rubber  tube  to  the  long  glass  tube  and  starting  the  siphon 
thus  formed,  the  water  in  the  bottle  will  be  siphoned  off  and 
air  drawn  in  to  take  its  place.  If  the  bottle  has  a  tubula- 
ture  at  the  bottom,  the  siphon  is  dispensed  with  and  water 
simply  drawn  off  at  the  bottom,  the  air  entering  at  the  top. 
A  water  suction  pump  will  practically  replace  the  aspi- 
rator, and  in  addition  is  invaluable  in  many  other  operations, 
such  as  rapid  filtration,  etc.  The 
glass  forms  are  less  liable  to  corro- 
sion, and  if  wound  with  several 
thicknesses  of  wire  gauze,  are  not 
easily  broken. 

A  combined  suction  pump  and 
water  blast  with  suitable  cocks  for 
regulating  the  suction  and  the 
strength  of  blast  is  of  great  value. 
The  expensive  metallic  forms  may 
be  replaced  by  the  less  convenient 
apparatus  (Fig.  1)  constructed  by  at- 
taching a  metal  or  glass  filter-pump 
to  one  neck  of  a  three-necked  one-liter  Wolff  bottle.  The 
middle  neck  is  fitted  with  a  rubber  stopper  and  a  glass  elbow, 


Fia.  1 


INTRODUCTION  7 

through  which  the  blast  of  air  is  discharged.  The  third 
neck  carries  a  cork  through  which  a  large  glass  tube  extend- 
ing to  the  bottom  of  the  Wolff  bottle  is  thrust.  The  upper 
part  of  the  glass  tube,  which  must  be  about  twice  as  high 
as  the  Wolff  bottle,  is  bent  downward  in  the  form  of  a  U, 
and  its  opening  so  directed  as  to  deliver  the  water  into  a 
sink  or  overflow.  On  allowing  water  to  flow  through  the 
filter-pump,  the  air  is  drawn  in,  and  the  air  and  the  water 
delivered  into  the  bottle,  the  water  collecting  in  the  bot- 
tom of  the  bottle.  If  the  air  exit  tube  in  the  middle  neck 
is  not  opened,  the  air  is  compressed  sufficiently  to  force  the 
water  out  of  the  bottle  through  the  tube  in  the  third  neck. 
Soon  the  water  will  have  been  so  far  removed  that  water 
mixed  with  air  is  forced  over.  By  opening  the  air-blast 
tube,  air  may  be  withdrawn  at  the  rate  desired,  provided  the 
level  of  the  water  in  the  bottle  does  not  rise  enough  to  flow 
out  of  the  air-tube.  With  a  good  strong  filter-pump  suffi- 
cient air  may  be  obtained  to  operate  a  blast-lamp. 

Pneumatic  troughs.  —  The  pneumatic  trough  is  indispen- 
sable in  experimenting  with  many  gases.  When  only  small 
quantities  of  a  gas  are  to  be  collected,  a  glass  crystallizing 
dish  is  used,  as  the  operation  is  then  entirely  visible. 
When  larger  quantities  are  to  be  operated  with,  a  zinc, 
galvanized  iron  or  copper  trough  is  used.  The  metal  should 
be  well  coated  with  asphalt  varnish  to  resist  the  action  of 
acids.  Sinks  and  troughs  set  in  the  lecture  table  are  a 
great  convenience,  but  by  no  means  indispensable. 


OXYGEN 


OXYGEN 

PREPARATION 

1.  From  mercuric  oxide.  —  Owing  to  its  historical  interest, 
this  exj5eriment  is  almost  invariably  used  in  introducing  the 
subject  of  oxygen. 

A  one-centimeter  layer  of  dry  mercuric  oxide  is  placed  in 
a  hard-glass  test-tube,  and  heated  in  a  Bunsen  burner  pro- 


V 

^ 

-_5qP 

1 

r#l#F^ 

vided  with  a  chimney.  The  tube  is  clamped  in  an  inclined 
position  nearly  horizontal,  and  the  burner  with  its  chimney 
so  arranged  (Fig.  2)  that  only  the  mercuric  oxide  is  heated, 
that  portion  of  the  test-tube  above  the  oxide  remaining  as 
cool  as  possible. 


OXYGEN  9 

By  using  a  somewhat  larger  portion  of  mercuric  oxide, 
and  fitting  a  cork  with  a  delivery-tube  into  the  mouth  of  the 
test-tube,  sufficient  oxygen  may  be  obtained  to  fill  several 
small  jars  at  the  pneumatic  trough. 

2HgO=2Hg  +  02. 
Bunsen  burner  and  chimney  ;  crystallizing  dish  and  cylinders  ;  HgO. 

2.  From  silver  oxide.  — Another  compound  of  oxygen  that 
is  easily  decomposed  by  heat  is  silver  oxide.  The  decompo- 
sition is  attended  by  a  characteristic  change  in  color  from 
the  brown  of  the  oxide  to  the  silver-white  of  the  metal. 

The  oxygen  is  evolved  in  such  considerable  quantities 
that  when  the  test-tube  is  fitted  with  a  delivery-tube,  several 
small  jars  of  oxygen  may  be  collected  at  the  pneumatic 
trough.  The  change  in  color  above  referred  to  especially 
recommends  the  method  for  lecture  use,  as  the  metallic  sil- 
ver is  easily  seen  at  a  distance.  If  the  heat  is  not  high 
enough  to  fuse  the  glass,  metallic  silver  in  a  semi-porous 
lump  may  be  shaken  out  of  the  test-tube  and  allowed  to  fall 
on  a  plate,  thus  further  showing  its  metallic  character. 

On  dissolving  the  residue  in  nitric  acid  and  precipitating 
with  an  excess  of  sodium  hydroxide,  hydrated  silver  oxide 
is  obtained,  which,  on  being  filtered  and  dried,  yields  the 
original  product  ready  for  a  repetition  of  the  experiment. 

2Ag20=4Ag  +  02. 

Test-tube  and  delivery-tube ;  several  60  cc.  cylinders ;  porcelain 
plate  ;  dry  Ag20. 

3.  By  heating  potassium  chlorate  in  the  presence  of  small 
quantities  of  other  oxides.  —  The  catalytic  action  of  manga- 
nese dioxide  and  ferric  oxide  on  molten  potassium  chlorate, 
causing  the  rapid  evolution  of  oxygen,  illustrates  the  advan- 


10  CHEMICAL    LECTURE    EXPERIMENTS 

tage  of  using  these  oxides  with  potassium  chlorate  in  the 
preparation  of  oxygen. 

Potassium  chlorate  is  melted  at  a  low  temperature  in  a 
hard-glass  tube,  and  the  absence  of  oxygen  shown  by  a 
glowing  taper.  The  salt  must  not  be  heated  much  above 
its  melting  point.  On  removing  the  lamp  and  immediately 
dropping  in  a  small  pinch  of  powdered  manganese  dioxide, 
a  vigorous  evolution  of  oxygen  ensues.  The  experiment 
may  be  repeated  with  another  tube  of  molten  potassium' 
chlorate,  using  ferric  oxide  instead  of  manganese  dioxide. 
The  demonstration  of  the  unchanged  nature  of  the  oxides  is 
not  adapted  to  lecture-table  experimentation. 

KCIO3  ;  MnOa  ;  FeaOg. 

4.  By  heatings  a  mixture  of  potassium  chlorate  and  man- 
ganese dioxide.  —  As  was  seen  in  the  preceding  experiment, 
the  presence  of  manganese  dioxide  influences  the  liberation 
of  oxygen  from  potassium  chlorate  in  two  ways :  first,  the 
temperature  at  which  oxygen  is  evolved  is  much  lower 
when  a  mixture  of  the  two  compounds  is  heated,  than 
when  the  potassium  chlorate  is  heated  by  itself;  second, 
the  evolution  of  oxygen  from  the  mixture  is  much  more 
regular.  Accordingly,  in  the  preparation  of  large  quanti- 
ties of  oxygen,  the  mixture  is  almost  invariably  used.  The 
two  ingredients  must  be  pulverized  and  thoroughly  dried. 

Twenty  grams  of  each  are  intimately  mixed  and  placed  in  a 
250  cc.  Jena  glass  Erlenmeyer  flask  fitted  with  a  cork  and  a 
rather  wide  glass  elbow,  and  clamped  on  a  ring-stand.  To 
the  elbow  is  attached  a  rubber  tube  fitted  with  a  glass  elbow 
at  the  other  end,  which  permits  of  a  free  movement  of  the 
tube  in  the  pneumatic  trough.  On  gradually  increasing  the 
heat,  a  rapid,  though  steady,  evolution  of  oxygen  ensues. 
The  gas  may  be  collected  in  several  glass  cylinders  for 
special  experiments,  or  may  be  transferred  to  one  of  the 


OXYGEN 


11 


many  forms  of  gas  holders.  At  the  end  of  the  reaction, 
the  tube  must  be  removed  from  the  pneumatic  trough  to 
prevent  the  back  suction  of  the  water.  The  purity  of  the 
manganese  dioxide  is  of  considerable  importance,  as  an 
admixture  of  carbonaceous  matter  of  any  nature  is  likely  to 
cause  an  explosion.  It  is  advisable  to  test  a  small  portion 
of  the  mixture  by  heating  it  in  a  test-tube.  If  glass  other 
than  Jena  is  used,  the  flask  should  be  protected  in  heating 
by  a  piece  of  asbestos  paper. 

2KC103=2KCl  +  3  02. 

250  cc.  Erlenmeyer  flask  (Jena)  ;  1-holed  rubber  cork  and  two  wide 
(7  mm.)  glass  elbows  ;  dry  Mn02  ;  KCIO3. 

5.  From  sodium  peroxide.  —  Water  decomposes  sodium 
peroxide  with  the  formation  of  sodium  hydroxide  and 
oxygen. 


^^zE 

v^^ 

_0— 

— 1 

^_.^..s-— . 

Fig.  3 


If  water  in  a  dropping-funnel  is  allowed  to  fall,  drop  by 
drop,  on  5  g.  of  dry  sodium  peroxide  in  a  dry  100  cc. 
Erlenmeyer  flask  fitted  with  a  delivery-tube  (Fig    3),   a 


12  CHEMICAL   LECTURE   EXPERIMENTS 

steady  evolution  of  pure  oxygen  is  secured.  The  yield 
of  oxygen  is  very  good,  6.25  g.  of  the  peroxide  giving 
1  1.  of  the  gas.  As  the  volume  of  the  ingredients  is 
small,  a  small  flask  is  used,  and  consequently  there  is  no 
great  volume  of  air  to  displace  before  beginning  to  collect 
the  product. 

The  advantages  of  this  method  of  preparing  oxygen  are 
numerous.  Peroxide  of  sodium,  while  but  recently  intro- 
duced into  the  market,  is  obtainable  at  a  very  reasonable 
price,  ranging  at  this  date  (1901)  from  75  cents  per  pound 
in  one-pound  packages  to  40  cents  per  pound  in  large 
quantities.  At  the  higher  price  the  cost  of  1  1.  of  oxygen 
prepared  in  this  manner  is  but  a  trifle  over  1  cent ;  there- 
fore the  method  is  in  no  sense  expensive.  However, 
owing  to  its  tendency  to  deteriorate  in  the  air,  sodium 
peroxide  must  be  preserved  in  tightly  stoppered  bottles, 
preferably  (in  case  of  long  standing)  sealed  with  a  little 
melted  paraffin.  The  apparatus  necessary  for  the  opera- 
tion is  extremely  simple,  and  as  no  heat  is  necessary, 
breakage  seldom  occurs. 

The  chemistry  of  the  reaction  is  certainly  no  more  com- 
plex to  the  elementary  student's  mind  than  that  .of  the 
potassium  chlorate  reaction,  especially  when  the  introduc- 
tion of  manganese  dioxide  must  be  explained  to  the  class. 

The  regulation  of  the  flow  of  oxygen  is  nearly  perfect,  as 
each  drop  of  water  generates  a  certain  amount  of  oxygen ; 
thus  a  few  centimeters  or  an  almost  unlimited  volume  per 
minute  can  be  obtained  by  simple  regulation  of  water  sup- 
ply. Only  a  small  quantity  of  water,  however,  is  necessary 
to  decompose  the  peroxide. 

2  NasOa  +  2  H2O  =  4  NaOH  +  O2. 

100  cc.  Erlenmeyer  flask ;  50  cc.  dropping-funnel ;  glass  elbow  ,• 
rubber  stopper ;   Na202. 


OXYGEN 


13 


6.  By  the  action  of  the  chlorophyl  of  green  leaves.  —  The 

exhalation  of  oxygen  by  green  leaves  under  the  influence 
of  sunlight  may  be  readily  shown  by 
filling  a  2  1.  flask  containing  green 
leaves  (not  too  closely  packed),  with 
water  through  which  carbon  dioxide 
has  been  allowed  to  bubble  (Fig.  4). 
A  large  funnel  is  passed  through  a  hole 
in  the  cork,  which  is  firmly  pressed 
down  into  the  flask  in.  such  a  manner 
that  the  carbon  dioxide  water  will  rise, 
thereby  expelling  the  air  in  the  stem 
of  the  funnel.  The  funnel  is  two- 
thirds  filled  with  water,  and  a  small  cyl- 
inder filled  with  water  is  inverted  with 
its  mouth  directly  over  the  stem  of  the 
funnel.  The  whole  apparatus  is  placed 
in  bright  sunlight,  and  in  a  few  hours 
sufficient  oxygen  will  have  risen  and  dis- 
placed the  water  in  the  small  cylinder  to 
give  a  good  test.  The  apparatus  may  be 
left,  and  the  oxygen  tested  at  the  next 
exercise.  If  the  carbon  dioxide  water  is 
not  too  strongly  charged  with  the  gas,  it  will  be  unneces- 
sary to  remove  the  trace  of  the  carbon  dioxide  from  the 
oxygen  before  testing. 

Apparatus  (Fig.  4)  ;  green  leaves  ;  carbon  dioxide  water. 


Fia.  4 


7.  From  the  electrolysis  of  copper  sulphate.  —  In  the  elec- 
trolysis of  copper  sulphate,  where  but  one  of  the  final 
products  of  electrical  decomposition  is  gaseous,  that  product, 
oxygen,  may  be  isolated  and  tested.  (Compare  with  the 
electrical  decomposition  of  water,  sodium  sulphate  solution, 
etc.,  where  two  gaseous  products  are  formed.) 


14 


CHEMICAL   LECTURE   EXPERIMENTS 


The  glass  bottle  of  the  electrolytic  apparatus  (Fig.  5)  is 
completely  filled  with  a  saturated  solution  of  copper  sul- 
phate, and  the  cork  inserted 
in  such  a  manner  as  to  drive 
out  all  the  air  and  fill  the  de- 
livery-tube with  the  solution. 
If  a  current  from  four  cells  of 
a  bichromate  battery  is  passed 
through  the  apparatus,  a  steady 
stream  of  oxygen  will  be  de- 
livered. One  of  the  platinum 
electrodes,  the  negative  one,  will  become  coated  almost  in- 
stantly with  metallic  copper;  the  other,  from  which  the 
bubbles  of  gas  rise,  will  retain  its  original  color. 

Pieces  of  cardboard  with  the  signs  +  and  —  are  placed 
in  a  proper  position  to  show  the  electrical  connection. 

2  CuSO,  +  2  H2O  =  2  Cu  +  2  H2SO4  +  O^. 
Electrolytic  apparatus  (Fig.  5)  ;  battery  ;  saturated  CUSO4  solution. 


Fig.  5 


8.  Compressed  oxygen.  —  No  gas  is  used  as  frequently  as 
oxygen  on  the  lecture  table.  Uniting,  as  it  does,  with 
almost  every  element,  in  most  instances  with  brilliancy, 
it  is  an  essential  factor  in  chemical  experimenting.  The 
method  of  obtaining  this  gas,  given  in  Ex.  5,  is  the  most 
advantageous  of  all  methods  involving  the  preparation  of 
the  gas,  but,  as  a  ready  supply  of  oxygen  for  lecture  table 
as  well  as  for  other  laboratory  purposes,  there  is  nothing  so 
satisfactory  and  reliable  as  a  cylinder  of  compressed  oxygen 
such  as  is  obtainable  in  the  market. 

Oxygen  as  ordinarily  used  in  the  laboratory  is  delivered 
from  a  gasometer  either  of  metal,  or  of  glass  with  metal 
connections.     These  gasometers,  owing  to  the  corrosive  action 


OXYGEN  15 

of  acids  and  fumes  in  the  laboratory,  soon  begin  to  leak,  and 
are  repaired  with  great  difficulty.  Furthermore,  their  chief 
use  is  to  store  either  air  or  oxygen,  as  the  Kipp  form  of 
generator  furnishes  a  steady,  constant  supply  of  many  gases 
such  as  hydrogen,  carbon  dioxide,  hydrogen  sulphide,  hydro- 
chloric acid  gas,  etc.  Since  by  means  of  the  water-blast  a 
steady  current  of  air  may  be  readily  obtained,  the  gasometer 
is  necessary  only  as  a  holder  of  oxygen.  The  cost  of  a 
Pepys  or  Mitscherlich  gasometer  is  very  considerable,  and 
for  a  much  less  sum  a  steel  cylinder  holding  10  cubic  feet  of 
oxygen  may  be  obtained.  By  simply  opening  the  valve  in 
the  top  of  the  cylinder,  the  gas  is  allowed  to  flow  out  at  any 
desired  rapidity  from  one  bubble  a  second  upward. 

A  so-called  "commercial  oxygen,"  which  has  slight  traces 
of  carbon  dioxide  and  nitrogen  as  impurities,  may  be  ob- 
tained from  the  S.  S.  White  Dental  Mfg.  Co.,  Princess  Bay, 
N.Y.,  at  the  very  reasonable  rate  of  ten  cents  per  cubic  foot. 
(One  cubic  foot  equals  28.3  1.)  This  gas  is  sufficiently 
pure  to  be  used  in  elementary  organic  analysis  after  being 
freed  from  the  small  amount  of  carbon  dioxide.  A  less 
pure,  though  for  experimental  purposes  equally  good,  oxygen 
may  be  obtained  from  the  dealers  in  calcium  light  supplies. 

A  pressure  regulator,  while  by  no  means  indis- 
pensable, is  of  great  advantage  in  using  a  cyl- 
inder of  compressed  gas.  Owing  to  its  cost, 
however,  its  use  is  not  likely  to  be  universal, 
and  recourse  must  be  had  to  a  simpler  device 
Avhich,  with  a  little  care,  gives  equally  satisfac- 
tory results.  The  stem  of  a  long  T-tube  is 
thrust  through  a  two-holed  rubber  stopper  which 
is  fitted  into  the  mouth  of  a  50  cc.  cylinder 
(Fig.  6).  The  tube  should  extend  nearly  to  the 
bottom  of  the  cylinder,  which  should  be  covered  with  a 
2  cm.  layer  of  mercury.     One  arm  of  the  T  is  connected  with 


1 

r^ 

1 

^ 

( 

Ji 

Wm/ 

i 

16  CHEMICAL   LECTURE   EXPERIMENTS 

the  oxygen  cylinder,  and  the  other  arm  is  connected  with 
the  apparatus  to  be  filled  by  means  of  a  rubber  tube  provided 
with  a  screw  pinch-cock. 

When  the  pinch-cock  is  open,  the  oxygen  flows  directly 
from  the  cylinder  through  the  T  into  the  vessel.  If  the 
pinch-cock  is  closed,  the  oxygen  flows  down  through  the 
stem  of  the  T  and  bubbles  through  the  mercury. 

In  many  cylinders  the  rate  of  the  issuing  gas  may  be  very 
accurately  controlled  by  the  operation  of  the  valve  in  the 
cylinder.  In  some,  however,  it  is  difficult  to  open  the  valve 
slowly  enough  to  prevent  a  sudden  rush  of  gas,  which  might 
prove  a  serious  difficulty  in  many  operations.  With  such 
cylinders  the  gas  is  conducted  through  the  T-tube,  one  arm 
of  which  is  closed.  The  rushing  gas  bubbles  through  the 
mercury  and,  by  closing  the  valve  on  the  cylinder,  the  cur- 
rent may  be  so  regulated  that  the  gas  slowly  bubbles  through 
the  mercury.  By  means  of  the  screw  pinch-cock  oxygen 
may  now  be  withdrawn  at  any  rate  desired.  It  is  always 
possible  so  to  regulate  the  pinch-cock  and  the  valve  on  the 
cylinder  that  no  gas  escapes  through  the  mercury. 

This  mercury  safety-bottle  serves  the  additional  purpose 
of  furnishing  a  vent  for  the  gas  in  case  the  tubes  of  the 
apparatus  used  for  the  experiment  become  clogged.  Soon 
the  pressure  would  rise  sufficiently  to  cause  the  gas  to 
bubble  through  the  mercury,  where  from  its  sound  it  would 
immediately  attract  attention.  It  is  unnecessary,  however, 
to  use  the  regulator  if  the  cylinder  is  provided  with  easily 
controlled  valves,  as  the  danger  resulting  from  the  stoppage 
of  tubes  is  very  slight. 

The  gas  may  be  collected  in  cylinders  over  water  or,  owing 
to  the  greater  density  of  oxygen,  it  may  be  collected  more 
conveniently  by  displacement  in  dry  jars.  A  glass  tube 
leading  to  the  bottom  of  the  jar  to  be  filled  is  connected 
with  a  rubber  tube  to  a  cylinder.     On  opening  the  valve  the 


OXYGEN  17 

gas  is  slowly  allowed  to  enter  the  jar  and,  as  it  rises,  push, 
out  the  air  at  the  top.  A  glass  plate  is  slipped  over  the 
mouth  of  the  jar,  and  a  glowing  splinter  held  at  the  opening 
beside  the  glass  tube.  When  the  jar  is  filled,  the  glowing 
taper  will  be  ignited.  The  gas  should  not  be  shut  off  until 
the  tube  is  withdrawn.  The  moment  the  end  of  the  glass 
tube  is  drawn  out  of  the  jar,  the  glass  plate  is  slipped  on  to 
seal  the  mouth  of  the  cylinder.  One  great  difficulty  in  fill- 
ing jars  by  this  method  is  the  fact  that  the  gas  is  often 
allowed  to  flow  at  too  rapid  a  rate,  thus  causing  air  currents 
inside  the  cylinder  and  a  consequent  test  for  oxygen  before 
the  jar  is  really  filled.  It  is  well  to  dip  the  end  of  the 
delivery-tube  into  water  for  an  instant  to  see  how  rapid 
the  flow  of  gas  is,  before  lowering  it  into  the  jar  to 
be  filled.  The  rate  of  flow  may  also  be  determined  by 
inserting  a  gas  washing-bottle  between  the  cylinder  and 
the  jar. 

Some  manufacturers  give  the  net  weight  of  the  cylinder 
as  well  as  the  weight  of  the  oxygen  it  contains.  In  such 
cases,  by  keeping  a  record  of  the  weight  of  the  cylinder,  it 
is  easy  to  determine  how  much  oxygen  remains  at  any 
given  time. 

PROPERTIES 

9.  Combustion  of  wood.  —  The  increased  brilliancy  of 
combustion,  as  well  as  the  rekindling  of  a  glowing  taper, 
may  be  shown  by  thrusting  a  splinter,  the  end  of  which  is 
glowing,  into  a  cylinder  of  oxygen.  The  experiment  may 
be  repeated  a  number  of  times,  and,  if  care  is  taken  not  to 
thrust  the  taper  too  deeply  into  the  jar,  and  not  to  let  it  re- 
main there  too  long  to  consume  the  oxygen,  it  will  be  seen 
that  at  each  repetition  the  splinter  must  be  thrust  a  little 
deeper  to  effect  rekindling. 

It  is  somewhat  difiicult  to  get  a  wood  that  will  retain  a 
c 


18  CHEMICAL   LECTURE   EXPERIMENTS 

spark,  though  splinters  made  from  cigar-box  wood  give  satis- 
factory results.  It  is  best,  in  extinguishing  the  flame  from 
the  burning  taper,  not  to  blow  it  out,  but  to  shake  it  out  by 
a  sudden  twist  of  the  hand,  as  in  this  way  the  spark  is  more 
likely  to  be  retained. 

10.  Combustion  of  a  candle.  —  Owing  to  the  fact  that 
there  are  considerable  quantities  of  gas  generated  in  the 
combustion  of  a  candle,  its  burning  in  oxygen  presents  a 
condition  slightly  different  from  that  where  a  splinter  is 
used.  If  the  candle  is  lowered  immediately  after  being 
blown  out,  the  gas  generated  by  the  still  hot  wick  will 
cause  a  slight  explosion  when  the  wick  is  rekindled,  espe- 
cially noticeable  if  the  oxygen  is  in  a  rather  tall  jar. 

Small  candle  on  wire  ;  jar  of  oxygen. 

11.  Combustion  of  charcoal.  —  Charcoal,  when  burning 
in  the  air,  gives  no  flame,  but  simply  glows.  In  oxygen  no 
flame  is  obtained,  though  the  glowing  may  approach  vivid 
incandescence. 

A  glass  cylinder  of  1  1.  capacity  is  filled  with  oxygen 
and  covered  with  a  glass  plate.  A  3  cm.  piece  of  char- 
coal, preferably  of  bark,  is  supported  in  a  loop  on  one 
end  of  a  stout  copper  or  iron  wire  some  40  cm.  in  length. 
On  heating  the  charcoal  in  a  Bunsen  burner  until  it  be- 
gins to  glow  and  then  quickly  introducing  it  into  the  jar 
of  oxygen,  the  increased  brilliancy  of  combustion  is  very 
marked.  If  the  copper  or  iron  wire  is  too  fine,  it  is  likely 
to  melt  or  burn  and  allow  the  charcoal  to  fall  to  the  bottom 
of  the  jar.  When  the  charcoal  ceases  to  glow,  the  wire  is 
withdrawn,  and  some  clear  limewater  poured  into  the  jar, 
the  glass  plate  replaced,  and  the  cylinder  shaken,  after 
which    the   contents   may   be    poured   into   a   glass.     The 


OXYGEN 


19 


limewater  is  cloudy,  with  a  white   precipitate  of  calcium 
carbonate. 

C+02=C02. 

3  cm.  piece  of  charcoal  on  wire  ;  1  1.  cylinder  of  oxygen  ;  lime- 
water. 

12.  Combustion  of  powdered  charcoal.  —  (a)  While  the 
combustion  of  a  solid  lump  of  charcoal  gave  no  apprecia- 
ble flame,  the  combustion  of  hot  finely  powdered  charcoal 
in  oxygen  is  attended  with  a  flame  of  intense  brilliancy. 
An  ordinary  iron  saucer,  such  as  is  used  for  a  sand  bath,  is 
one-third  filled  with  finely  powdered  charcoal  (willow  char- 
coal is  the  best)  and  heated  until  the  charcoal  just  begins 
to  glow  in  spots.  A  grocer's  sugar 
funnel  or  an  ordinary  glass  funnel, 
cut  so  as  to  make  the  frustum  of 
a  cone,  is  quickly  slipped  into  the 
mouth  of  a  cylinder  of  oxygen  of 
not  less  than  1 1.  capacity.  The  red- 
hot  charcoal  is  immediately  poured 
from  the  iron  dish  into  the  funnel, 
care  being  taken  to  use  the  crucible 
tongs  and  to  protect  the  hands 
with  gauntlets.  The  face  should 
not  be  held  too  near  the  jar,  as  the  flame  reaches  a  consid- 
erable height.  When  the  hot  charcoal  falls  through  the 
oxygen,  the  combustion  is  of  almost  explosive  violence  and 
dazzling  brilliancy  (Fig.  7). 

Large  wide-mouthed  bottle  or  jar  of  oxygen  (Fig.  7)  ;  grocer's 
tin  sugar  funnel  ;  powdered  willow  charcoal ;  iron  dish  ;  crucible 
tongs  ;  gauntlets. 

(b)  A  stream  of  oxygen,  when  allowed  to  play  on  glowing, 
powdered  charcoal,  produces  a  most  vivid  combustion. 
Finely  powdered  willow  charcoal  is  placed  in  a  small  iron 


Fig.  7 


20 


CHEMICAL   LECTURE   EXPERIMENTS 


dish  (sand  bath)  and  heated  until  the  surface  begins  to  glow. 

The  flame  is  then  removed,  and  a  stream  of  oxygen  is  passed 
through  a  long  glass  tube  with  a 
bend  at  the  end  and  allowed  to 
play  over  the  surface  of  the  glow- 
ing charcoal.  The  combustion  be- 
comes very  vivid,  and  if  the  stream 
of  oxygen  is  of  sufficient  force  to 
blow  the  dust  out  of  the  dish,  the- 
brilliancy  of  the  combustion  is 
almost  blinding  (Fig.  8). 


Fig.  8 


Iron  dish  (sand  bath)  ;  powdered  wil- 
low charcoal  :  current  of  O. 


13.  Combustion  of  sulphur.  —  A  porcelain  crucible  about 
the  size  of  a  thimble  is  so  suspended  in  a  loop  of  stout  iron 
wire  that  it  may  be  lowered  into  a  jar  of  oxygen.  The 
crucible  is  three-fourths  filled  with  small  bits  of  lump  sul- 
phur which  are  heated  to  boiling.  On  lowering  the  burning 
sulphur  into  a  500  cc.  jar  of  oxygen,  the  combustion  is  con- 
tinued with  great  brilliancy,  resulting  in  the  production 
of  a  blue  flame.  That  the  product  of  combustion  differs 
materially  from  oxygen  may  be  shown  either  by  bleaching 
moistened  blue  litmus  paper  or  by  thrusting  a  piece  of 
filter-paper  moistened  with  potassium  dichromate  solution 
into  the  jar.  In  the  latter  case  the  red  color  of  the  dichro- 
mate is  turned  deep  green  by  reduction. 

S  +  O2  =  SO2. 

Small  porcelain  crucible  and  stout  iron  wire ;  500  cc.  jar  of 
oxygen  ;    lump  sulphur  ;   K2Cr207  solution. 

14.  Combustion  of  phosphorus.  —  (a)  The  brilliancy  of 
the  combustion  of  phosphorus  in  oxygen  is  so  great  that  this 
experiment  has  frequently  been  termed  the  "mock  sun." 


I 


OXYGEN  21 

A  5  mm.  piece  of  phosphorus,  which  has  been  carefully 
dried  between  filter-paper,^  is  placed  in  a  small  deflagrating 
spoon  and  a  short  piece  of  cotton  twine  laid  beside  it  in 
such  a  manner  that  when  a  spark  is  started  at  the  end  of 
the  twine  it  will  serve  as  tinder  to  light  the  phosphorus 
on  its  introduction  into  the  oxygen.  The  oxygen  is  held  in 
a  large  flask  or  bottle,  the  bottom  of  which  is  covered  with 
a  little  water.  The  deflagrating-spoon  is  previously  arranged 
to  allow  the  phosphorus  to  burn  near  the  bottom  of  the 
vessel.  On  lowering  the  deflagrating-spoon  into  the  jar,  the 
glowing  bit  of  twine  bursts  into  a  flame,  which  is  immedi- 
ately communicated  to  the  phosphorus,  and  the  combustion 
continues  with  dazzling  brilliancy.  White  clouds  of  phos- 
phorus pentoxide  fill  the  whole  jar,  and  by  reflection  of  the 
light  make  the  interior  of  the  vessel  luminous.  If  the  flask 
was  filled  with  oxygen  by  the  displacement  of  air  and  the 
interior  is  dry,  the  phosphorus  pentoxide  will  settle  as  a 
white  hygroscopic  powder  all  over  the  interior  of  the  flask. 
In  this  case,  however,  it  is  advisable  to  place  a  layer  of 
sand  in  the  bottom  of  the  vessel.  A  very  small  flame 
should  be  used  to  start  a  spark  on  the  twine,  and  care  taken 
to  prevent  a  premature  ignition  of  the  phosphorus. 

P,  H-  5  O2  =  2  P2O,. 

Large  flask  or  jar  of  oxygen  ;  deflagrating-spoon  ;  cotton  twine  ;  P. 

(6)  The  diminution  in  volume  of  the  gas  by  the  com- 
bustion of  phosphorus  in  oxygen  is  shown  by  using  an 
apparatus  similar  to  that  of  Fig.  78,  p.  182.  The  liter 
bell-jar  used  in  this  experiment  should  be  tubulated.  A 
crucible  cover  containing  .5  g.  of  red  phosphorus  is  placed 
on  a  large  cork  floating  on  the  surface  of  water  in  a 
pneumatic  trough.  The  bell-jar  is  then  placed  over  the 
float,  and   by  removing  the  stopper  oxygen  is  conducted 

1  For  precautions  in  handling  phosphorus,  see  p.  232. 


22 


CHEMICAL  LECTURE  EXPERIMENTS 


into  the  jar,  thereby  driving  out  the  air.  When  all  the  air 
has  been  removed  and  a  good  test  for  oxygen  obtained  at 
the  mouth  of  the  bell-jar,  a  bit  of  string  or  paper  which  has 
previously  been  ignited  is  dropped  upon  the  crucible  lid, 
which  has  been  brought  under  the  opening  in  the  bell-jar 
by  means  of  a  long  wire.  The  cork  is  then  immediately 
inserted.  As  the  phosphorus  burns,  the  water  rises  in  the 
jar,  and  it  will  thus  be  seen  that  a  considerable  quantity  of 
oxygen  will  be  consumed. 

Cork  ;  crucible  lid  ;  tubulated  liter  bell-jar  ;  string  ;  red  P. 

15.  Quantitative  combustion  of  phos- 
phorus in  oxygen.  — Phosphorus  burning 
in  oxygen  forms  phosphorus  pentoxide, 
a  white  powder,  which  weighs  consider- 
ably more  than  the  phosphorus  used. 
The  increase  in  weight  is  shown  by 
burning  the  phosphorus  in  a  confined 
volume  of  oxygen  in  such  a  manner  that 
the  product  of  combustion  is  retained. 

A  dry  two-liter  flask  is  filled  with 
oxygen  and  fitted  with  a  one-holed  rub- 
ber stopper  carrying  a  20  cm.  length  of 
glass  tubing,  7  mm.  in  diameter,  which 
is  loosely  filled  with  coarse  glass  wool 
or  asbestos  (Fig.  9).  A  stout  copper 
wire  is  fastened  to  the  stopper  with  the 
lower  end,  which  is  provided  with  a 
loop  in  which  a  small  crucible  is  placed, 
near  the  bottom  of  the  flask.  The  cru- 
cible should  not  contain  more  than  1  or 
2  cc,  and  should  be  about  two-thirds 
filled  with  red  phosphorus.  One  end  of  a  2  cm.  length 
of   string  is  inserted  in   the   phosphorus  in  such  a  man- 


FiG.  9 


OXYGEN  23 

iier  that  the  other  end  may  be  ignited  in  the  air.  The 
system  is  then  brought  into  equilibrium  on  the  lecture- 
balance.  The  stopper  is  removed,  care  being  taken  not  to 
disturb  the  crucible  or  contents,  the  string  ignited,  and  the 
stopper  again  thrust  into  the  flask,  where  the  string  com- 
municates the  fire  to  the  phosphorus,  which  in  turn  burns 
with  a  bright  flame.  The  glass  wool  prevents  the  exit  of 
the  phosphorus  pentoxide,  which  remains  as  a  dry  white 
powder  covering  the  bottom  and  a  portion  of  the  sides  of 
the  flask.  After  a  few  minutes  the  increase  in  weight  of 
the  system,  amounting  to  about  .5  g.,  will  be  very  apparent. 

Lecture-balance  ;  cork  and  tube  with  glass  wool ;  copper  wire ; 
small  crucible  ;  string  ;  0  supply  ;  red  P. 

16.   Combustion    of    "steel  wool"   in  oxygen.  —  Of  the 

numerous  forms  of  finely  divided  iron,  that  best  adapted 
for  combustion  in  oxygen  is  the  so-called  "  steel  wool  "  or 
steel  fibre,  which,  as  the  name  indicates,  is  a  mass  of  fine 
shreds  of  steel.  This  product  is  used  extensively  for  polish- 
ing hardwood,  and  is  accordingly  obtainable  from  most 
dealers  in  hardware  or  painters'  supplies.  A  German  prod- 
uct, which  is  sold  only  in  pound  packages,  is  but  very  little, 
if  any,  better  than  the  American  product,  which  can  be  ob- 
tained in  quantities  as  small  as  desired. 

A  bit  of  the  wool  heated  in  the  air  will  continue  to  burn 
for  a  few  moments. 

It  is  in  pure  oxygen,  however,  that  the  brilliancy  of  the 
combustion  is  best  observed.  A  tuft  of  the  wool  is  fastened 
on  the  end  of  a  stout  iron  wire,  heated  in  the  Bunsen  flame 
to  incipient  combustion,  and  then  thrust  into  a  jar  of  oxygen, 
on  the  bottom  of  which  a  layer  of  water,  sand,  or  asbestos 
paper  is  provided.  The  wool  burns  with  beautiful  scintilla- 
tions, the  iron  oxide  falling  to  the  bottom  in  fused  globules. 

Jar  of  O  with  H2O,  sand,  or  asbestos  ;  "  steel  wool." 


24  CHEMICAL   LECTURE   EXPERIMENTS 

17.  Combustion  of  aluminium.  —  Aluminium  in  the  form 
of  thin  leaf  is  as  combustible  in  oxygen  as  magnesium  or 
any  of  the  other  finely  divided  metals,  while  in  air  it  is 
not  easily  ignited. 

Three  or  four  leaves  of  aluminium  are  loosely  bound 
with  a  stout  iron  wire  and  lowered  into  a  jar  of  oxygen. 
A  centimeter  piece  of  twine  fastened  to  the  loop  of  the  iron 
wire  and  ignited  an  instant  before  being  thrust  into  the  jar 
serves  to  kindle  the  aluminium  leaf.  The  combustion  is 
instantaneous  and  accompanied  by  a  bright  flash.  If  the 
iron  wire  is  too  fine,  it  also  will  burn  in  the  oxygen. 

Aluminium  leaf  ;  300  cc.  cylinder  of  0. 

18.  Combustion  of  finely  divided  magnesium,  aluminium, 
zinc,  or  iron  in  oxygen.  —  The  brilliancy  of  the  combustion 
of  these  metals  in  oxygen  is  shown  by  causing  each  of 
them  to  be  blown  lengthwise  through  the  Bunsen  flame  by 
a  sudden  puff  of  oxygen.  Each  powder  is  placed  in  the 
bend  of  a  glass  elbow,  of  5  or  6  mm.  internal  diameter,  in 
such  a  way  that  it  does  not  quite  obstruct  the  passage  of 
the  gas  through  the  tube.  A  very  gentle  stream  of  oxygen 
is  allowed  to  flow  through  the  elbow  over  the  metal  till  all 
the  air  is  driven  out.  On  directing  the  open  end  of  the 
elbow  toward  the  Bunsen  flame,  and  suddenly  admitting  a 
puff  of  oxygen  or  air,  the  greater  portion  of  the  powdered 
metal  will  be  shot  across  or  through  the  flame  and  there  be 
burnt  with  a  blinding  flash.  The  elbow  should  be  so  directed 
that  the  powder  will  be  blown  through  the  length  of  the 
flame.  As  considerable  care  is  necessary  to  secure  the 
proper  introduction  of  the  metal  into  the  glass  elbow,  it  is 
advisable  to  have  prepared  four  elbows,  all  properly  filled 
with  the  respective  powders. 

Four  glass  elbows  (6  mm.  diameter)  ;  Mg,  Al,  and  Fe  powders ; 
Zn  dust. 


OXYGEN 


25 


m 


m 


'■','///■ 


■ 


19.  Explosion  of  a  mixture  of  powdered  charcoal  and 
oxygen.  — Oxygen  ladened  with  charcoal  dust  forms  an  ex- 
plosive mixture  which  varies  in  violence  with  the  amount 
of  dust  suspended  in  the  gas.  Variations  in  the  rapidity  of 
combustion  may  be  easily  studied  by  means  of  the  following 
experiment :  — 

A  5  mm.  layer  of  finely  powdered  willow  charcoal  is 
placed  in  the  bottom  of  a  dry  500  cc.  cylinder.  A  stream 
of  oxygen  is  directed  through  a  glass  tube  which  extends 
to  the  bottom  of  the  glass  cylinder  and  is 
bent  at  right  angles  3  cm.  above  the  mouth 
of  the  cylinder  (Fig.  10)  in  such  a  manner  h 
that  the  current  of  gas  stirs  up  the  char- 
coal powder  in  the  bottom  of  the  cylinder 
and  fills  it  with  a  dust-ladened  atmosphere 
of  oxygen.  The  oxygen  is  then  cut  oif 
and  a  flame  instantly  applied  at  the  mouth 
of  the  cylinder.  By  varying  the  rapidity 
of  the  current  of  oxygen,  and  consequently 
the  proportion  of  the  dust  in  the  gas,  the 
flame  may  be  made  to  travel  down  the 
cylinder  with  varying  degrees  of  velocity,  Fiq.  lo 

affording  an  interesting  study  of  the  rate 
of  propagation  of  an  explosion.     This  and  the  following 
experiment  are  striking  illustrations  of  the  explosion  of 
a  solid  in  a  gas. 

500  cc.  cylinder  ;  powdered  willow  charcoal ;  current  of  O. 


4 


20.  Explosive  combustion  of  powdered  iron,  aluminium,  or 
zinc  in  oxygen.  —  An  atmosphere  of  oxygen  ladened  with 
the  dust  of  iron,  aluminium,  or  zinc,  possesses  explosive 
properties. 

Oxygen  is  conducted  through  a  bent  glass  tube  to  the 
bottom  of  a  glass  cylinder,  3  cm.  in  diameter  and  15  cm. 


« 


26        CHEMICAL  LECTURE  EXPERIMENTS 

high.  A  5  mm.  layer  of  powdered  iron  or  aluminium  or  zinc 
dust  is  placed  on  the  bottom  of  the  jar.  The  stream  of 
oxygen  is  so  directed  as  to  blow  the  dust  up  into  the  cyl- 
inder and  produce  an  atmosphere  of  oxygen  ladened  with 
the  metallic  dust.  On  applying  a  flame  at  the  mouth  of  the 
cylinder  the  mixture  explodes.  The  brilliancy  of  the  com- 
bustion renders  the  use  of  colored  glasses  necessary. 

100  cc.  glass  cylinder  ;  colored  glasses  ;  current  of  O  ;  powdered  Fe, 
Al ;  Zn  dust. 

21.  Absorption  of  oxygen  by  potassium  pyrogallate.  — 

Oxygen  is  collected  in  a  eudiometer  (Fig.  11),  and  potassium 
pyrogallate  solution  is  allowed  to  flow  down  through 
the  stopcock  into  the  gas.  The  absorption  of  the 
oxygen  is  almost  immediate,  the  water  rising  to 
take  the  place  of  the  absorbed  gas. 

Potassium  pyrogallate  solution  is  best  made  by 
dissolving  10  g.  of  pyrogallic  acid  in  a  solution  of 
100  g.  of  stick  potassium  hydroxide  in  500  cc.  of 
water.  Made  with  these  proportions  the  solution 
absorbs  oxygen  readily  and,  if  tightly  corked,  keeps 

Fig.  11     well. 

Eudiometer  (Fig.  11)  ;  pyrogallic  acid  ;  stick  KOH  ;  0. 

22.  Combustion  of  zinc  in  air.  —  At  the  ordinary  temper- 
ature it  is  extremely  difficult  to  ignite  zinc,  though,  when  at 
or  near  its  boiling  point,  combination  with  the  oxygen  of 
the  air  takes  place  easily. 

Three  or  four  grams  of  zinc  (not  granulated)  are  heated 
in  a  small  porcelain  crucible  with  a  blast-lamp.  After  a  few 
minutes  the  zinc  boils  and  catches  fire  on  the  surface.  The 
zinc  oxide  formed  collects  in  white  flocks  around  the  edge  of 
the  crucible,  which,  on  cutting  off  the  blast,  ascend  with  the 


OXYGEN  27 

hot  current  of  air  in  white  clouds.  On  cooling,  the  floccu- 
lent  nature  of  the  zinc  oxide  may  be  observed. 

2  Zn  +  O2  =  2  ZnO. 

Crucible  ;  blast-lamp  ;  Zn. 

23.  Combustion  of  iron  in  air  (quantitative  experiment). — 

A  small  magnet  to  which  a  considerable  quantity  of  iron 
powder  is  hanging  is  suspended  from  one  arm  of  a  lecture- 
balance  which  is  brought  into  equilibrium.  The  iron  is 
then  ignited  by  gently  playing  a  Bunsen  flame  upon  it,  care 
being  taken  not  to  disturb  the  balance.  In  a  few  moments 
sufficient  oxygen  will  have  combined  with  the  iron  to  pro- 
duce a  very  considerable  change  in  the  equilibrium  of  the 
balance. 

A  much  larger  amount  of  iron,  consequently  showing  a 
greater  deflection,  can  be  burned  by  placing  the  iron  powder 
on  a  square  of  sheet  asbestos  that  has  previously  been 
ignited.  The  asbestos  is  placed  on  a  square  of  wire  gauze, 
and  so  laid  on  the  balance  pan  as  to  prevent  undue  heating 
and  consequent  unsoldering  of  its  supports.  The  balance  is 
then  brought  into  equilibrium,  and  the  iron  ignited  by  means 
of  a  small  gas-jet.  The  combustion  continues  of  itself,  and 
soon  a  large  deflection  of  the  balance  is  noticeable. 

Magnet ;  lecture-balance  ;  ignited  asbestos  paper  ;  square  of  wire 
gauze ;  iron  powder. 

24.  Combustion  of  magnesium  in  air  (quantitative  exper- 
iment). —  Magnesium  powder  burns  quietly  in  the  air,  form- 
ing white  magnesium  oxide. 

Five  grams  of  magnesium  powder  are  heaped  on  a  12  cm. 
square  of  previously  ignited  asbestos  paper,  which  is  in  turn 
placed  on, the  pan  of  a  lecture-balance,  with  all  the  pre- 
cautions of  the  preceding  experiment.     After  bringing  the 


28 


CHEMICAL   LECTURE   EXPERIMENTS 


system  to  equilibrium,  the  magnesium  is  ignited  with  a 
match  or  gas-jet.  The  combustion  soon  proceeds  through 
the  whole  mass,  which  increases  in  volume  considerably, 
and  a  small  portion  of  the  magnesium  oxide  formed 
escapes  as  a  white  smoke.  After  the  mass  has  become 
cool,  approximately  2  g.  will  be  required  to  restore  the 
equilibrium. 

Lecture-balance  ;  wire  gauze  ;  asbestos  paper ;  Mg  powder. 

25.   Increase  in  weight  by  the  combustion  of  a  candle  in 
air.  —  In  burning  a  candle,  if  provision  is  made  to  collect 
the  products  of  combustion,  i.e.,  carbon  di- 
oxide and  water,  it  will  be  found  that  they 
weigh  more  than  the  candle  consumed. 

A  cylindrical  Argand  lamp  chimney,  21 
cm.  high,  5.5  cm.  in  diameter,  is  provided 
with  a  false,  wire  gauze  bottom,  as  is  shown 
in  Fig.  12.  A  circular  piece  of  rather 
coarse  wire  gauze  is  cut  of  such  a  size  as  to 
readily  pass  through  the  chimney.  Three 
pieces  of  fine  copper  wire,  50  cm.  long,  are 
fastened  at  three  equidistant  points  in  the 
circumference  of  the  gauze  by  tying  a  knot 
in  the  middle  of  each  of  the  three  strands. 
The  gauze  bottom  is  placed  inside  the 
chimney  6  cm.  from  one  end,  and  fastened 
in  this  position,  by  bringing  the  wires  up 
on  the  outside  as  well  as  the  inside  of  the 
chimney  and  twisting  the  ends  of  each  wire 
together  at  the  top.  One  end  of  each  strand 
is  left  long  enough  to  twist  all  three  to- 
gether and  form  a  suspension  for  the  chim- 
ney. A  few  lumps  of  quicklime  are  placed  on  top  of  the 
wire  gauze  and  the  rest  of  the  space  nearly  filled  with  stick 


Fig.  12 


OXYGEN  29 

sodium  hydroxide.  A  large  cork  is  fitted  to  the  lower  part 
of  the  chimney.  Several  good-sized  holes  are  made  through 
the  cork  to  allow  for  the  draft,  and  the  ring  of  a  crucible 
lid  is  pressed  into  a  slit  in  the  centre  of  the  cork,  forming  a 
pan  on  which  a  candle  is  placed.  The  whole  apparatus  is 
suspended  on  the  arm  of  a  lecture-balance  and  brought  into 
equilibrium.  The  cork  is  removed,  the  candle  lighted,  and 
the  cork  quickly  replaced.  If  the  holes  in  the  cork  are  of 
sufficient  size,  there  will  be  a  good  draft  and  the  candle  will 
burn  freely.  The  candle  is  of  ordinary  size  and  rather 
short,  about  15  mm.  high.  Any  wax  dropping  from  the 
candle  is  caught  in  the  crucible  cover.  The  holes  in 
the  cork  can  be  made  by  cutting  V-shaped  sections  out  of 
the  edge.  After  burning  a  few  minutes  a  very  perceptible 
increase  in  weight  will  be  obtained. 

Argand  lamp  chimney ;  wire  gauze ;  lecture-balance ;  Cu  wire 
(fine)  ;  quicklime ;  stick  NaOH. 

26.  Quantitative  combustion  of  phosphorus  in  air. — The 

apparatus  of  Ex.  15  may  be  used  to  demonstrate  the  in- 
crease in  weight  of  phosphorus  burning  in  air. 

It  is  better  to  substitute  yellow  for  red  phosphorus  and 
to  induce  the  ignition  by  a  strip  of  touch-paper  (p.  355). 
A  7  mm.  piece  of  well-dried  phosphorus  is  placed  in  the 
crucible  on  top  of  a  piece  of  touch-paper  which  protrudes 
some  2  or  3  cm.  above  the  top  of  the  crucible.  The 
apparatus  is  then  carefully  tared,  as  before,  the  cork  re- 
moved, and  the  touch-paper  ignited.  The  time  required  for 
the  touch-paper  to  communicate  the  flame  to  the  phosphorus 
is  generally  sufficient  to  permit  the  insertion  of  the  cork 
and  the  adjusting  of  the  balance. 

The  phosphorus  pentoxide  formed  settles  to  the  bottom 
and  sides  of  the  flask  as  a  dry,  white  powder. 

After  the  combustion  is  complete,  and  the  system  has 


30  CHEMICAL  LECTURE  EXPERIMENTS 

reached  the  room  temperature,  an  increase  in  weight  of 
.6  g.  will  be  obtained. 

Apparatus  (Ex.  15.)  ;  0  supply  ;  yellow  P ;  touch-paper. 

27.  Increase  in  weight  by  burning  sulphur  in  the  air. 

—  If  the  sulphur  dioxide  formed  by  burning  sulphur  could 
be  collected,  its  weight  would  be  exactly  twice  that  of  the 
sulphur  used.  By  means  of  a  slight  modification  of  the 
apparatus  of  Fig.  12,  p.  28,  the  increase  in  weight  by  burn- 
ing sulphur  in  the  air  may  be  easily  demonstrated,  though 
it  is  impossible  to  make  the  experiment  so  far  quantitative 
as  to  show  any  mathematical  relation  between  the  weight  of 
the  sulphur  and  the  weight  of  the  product. 

The  Argand  lamp  chimney,  prepared  and  filled  with 
quicklime  and  sodium  hydroxide,  as  described  in  Ex.  25,  is 
provided  with  a  perforated  cork  carrying  a  crucible  cover,  a 
small  disk  of  asbestos  paper  being  placed  between  the  cork 
and  the  crucible  cover.  A  few  bits  of  sulphur  are  placed  in 
the  crucible  lid,  the  cork  inserted  in  the  chimney,  and  the 
whole  brought  to  equilibrium  on  the  lecture-balance.  The 
cork  is  then  removed,  the  sulphur  ignited,  and  the  cork 
replaced  in  the  chimney.  It  is  advisable  to  let  the  sulphur 
burn  in  the  air  for  a  moment  or  two  to  insure  its  thorough 
ignition.  The  sulphur  burned  by  so  waiting  interferes  in 
no  way  with  the  experiment.  A  few  minutes  after  the 
cork  is  replaced  in  the  chimney  a  marked  increase  in  weight 
is  observed. 

Lamp  chimney  filled  with  lime  and  NaOH  ;  cork  with  asbestos  disk 
and  crucible  cover  ;  S. 

28.  Absorption  of  oxygen  by  rusting  iron.  —  The  absorp- 
tion of  oxygen  from  the  air  by  rusting  iron  can  be  readily 
effected  by  inserting  a  wad  of  steel  wool  (Ex.  16)  into  a 
eudiometer  tube  containing  100   cc.    of  air,  inverted  over 


I 

-^ 

E^ 

^ 

bp 

OZONE  31 

a  crystallizing  dish  of  water  (Fig.  13).  The  eudiometer 
should  first  be  filled  with  water  and  then  enough  of  the 
water  allowed  to  flow  out  of  the  tube  to  confine 
about  100  cc.  of  air.  The  plug  of  steel  wool  is 
then  thrust  under  water  and  inserted  in  the  tube 
by  means  of  a  long  copper  wire. 

The  apparatus  thus  prepared  is  allowed  to 
stand  twenty-four  hours,  when  it  will  be  seen 
that  the  iron  has  rusted  considerably  and  that 
the  volume  of  the  enclosed  gas  has  materially 
diminished. 

Eudiometer  tube  ;  steel  wool ;  Cu  wire.  Fig.  13 

OZONE 

FORMATION   AND   PREPARATION 

29.  By  heating  potassium  chlorate  or  mercuric  oxide. — 

If  a  small  quantity  of  potassium  chlorate  or  mercuric  oxide 
is  heated  in  a  hard-glass  tube  until  oxygen  is  evolved,  a 
piece  of  moistened  iodo-starch  paper  held  at  the  mouth  of 
the  tube  will  be  turned  a  deep  blue. 

KC103  =  KCl+03.    [?] 
3HgO  =  3Hg+03.  [?] 
KCIO3  ;  HgO  ;  Kl-starch  paper. 

30.  From  barium  peroxide  and  sulphuric  acid.  —  By  act- 
ing on  a  peroxide  with  a  strong  acid,  ozone  is  formed  in 
very  appreciable  quantities. 

Three  or  four  grams  of  powdered  barium  peroxide  are 
carefully  and  gradually  shaken  into  a  small  beaker  containing 
10  cc.  of  concentrated  sulphuric  acid  externally  cooled  by 
ice.  The  air  immediately  above  the  beaker  is  very  rich  in 
ozone  and  will  give  any  of  the  usual  tests. 


32  CHEMICAL   LECTURE   EXPERIMENTS 

In  this  experiment  the  process  may  be  reversed  by  drop- 
ping the  cooled  sulphuric  acid  upon  the  barium  peroxide  in 
the  bottom  of  the  externally  cooled  beaker. 

3  BaOs  +  3  H2SO4  =  3  BaSO^  +  3  H^O  +  O3.  [?] 
Ba02;  ice. 

31.  By  the  action  of  sulphuric  acid  on  potassium  perman- 
ganate. —  As  the  action  of  concentrated  sulphuric  acid 
liberates  chromic  anhydride  from  potassium  dichromate 
(Ex.  2,  p.  405),  in  like  manner  permanganic  anhydride  is 
liberated  from  potassium  permanganate. 

Permanganic  anhydride,  owing  to  its  unstable  nature,  im- 
mediately decomposes  into  manganese  dioxide  and  ozone, 
the  latter  being  obtained  in  considerable  quantities.  This 
reaction  is  very  violent,  and  consequently  must  be  performed 
on  a  small  scale  only.  It  may  be  safely  carried  out,  how- 
ever, by  placing  1  g.  of  powdered  potassium  permanganate 
in  each  of  six  small  beakers  standing  in  a  large  crystallizing 
dish,  the  bottom  of  which  is  covered  with  a  centimeter  layer 
of  water.  The  potassium  permanganate  in  the  beakers  is 
moistened  with  a  few  drops  of  water. 

Into  one  of  the  beakers  2  cc.  of  concentrated  sulphuric 
acid  are  poured.  A  vigorous  reaction  takes  place,  accom- 
panied by  a  smoke  consisting  chiefly  of  brown  manganese 
dioxide.  A  pinch  of  sulphur  flowers  dropped  into  the 
beaker  is  instantly  ignited. 

The  second  beaker  is  likewise  treated  with  2  cc.  of  con- 
centrated sulphuric  acid,  and  a  small  piece  of  phosphorus 
thrown  into  it.     The  combustion  is  instantaneous. 

Into  the  third  beaker,  after  the  addition  of  sulphuric  acid, 
1  cc.  of  alcohol  is  poured  from  a  test-tube  fastened  to  the 
end  of  a  long  stick.  The  combustion  is  of  almost  explosive 
violence. 


OZONE  33 

A  polished  silver  coin,  held  by  tongs  above  the  mixture  in 
the  fourth  beaker,  is  rapidly  turned  black,  giving  the  char- 
acteristic ozone  test.  Then  a  slow  stream  of  illuminating 
gas  is  allowed  to  pass  through  a  glass  tube  held  at  the  mouth 
of  the  beaker.  It  is  ignited,  and,  by  pinching  the  rubber 
tube,  the  flame  may  be  extinguished  and  relighted  a  number 
of  times. 

A  glass  rod  is  dipped  in  the  mixture  in  the  fifth  beaker, 
and  then  touched  to  the  wick  of  an  alcohol  lamp.  The 
oxidizing  mixture  adhering  to  the  glass  rod  lights  the  lamp. 

Four  cubic  centimeters  of  ether  are  poured  from  a  test- 
tube  along  the  floor,  and  one  end  of  the  moistened  strip 
touched  with  a  glass  rod  dipped  in  the  fresh  mixture  pre- 
pared in  the  sixth  beaker.  The  ether  is  ignited,  and  the 
flame  travels  along  the  floor.  As  but  a  few  cubic  centimeters 
of  ether  are  used,  the  combustion  is  of  short  duration  and 
harmless.  As  the  ether  burns,  it  will  be  seen  that  the  vapor 
has  rolled  out  on  either  side  of  the  moistened  strip. 

In  all  these  experiments,  protection  is  necessary  from  fly- 
ing drops  of  concentrated  sulphuric  acid  that  might  spurt 
from  the  beakers  in  such  vigorous  reactions.  After  use, 
each  beaker  should  be  removed  with  crucible  tongs,  and 
plunged  into  a  dish  of  water  kept  at  hand  for  that  purpose= 

2  KMn04  H-  H2SO4  =  K2SO4  -f-  MugO;  -f  HgO. 
MnA  =  2  MnOo  +  O3. 

Six  50  cc.  beakers  ;  large  evaporating  dish  filled  with  water  ;  large 
crystallizing  dish  ;  test-tube  on  a  long  stick  ;  pulverized  KMn04  ;  S 
flowers  ;  small  piece  of  P  ;  alcohol  and  alcohol  lamp  ;  ether. 

32.  By  slow  oxidization  of  phosphorus.  —  When  moist 
phosphorus  is  allowed  to  remain  in  contact  with  air,  it  is 
slowly  oxidized,  and  a  portion  of  the  oxygen  of  the  air 
is  converted  to  ozone. 

D 


34 


CHEMICAL   LECTURE   EXPERIMENTS 


A  few  sticks  of  freshly  scraped  phosphorus,  about  4  cm. 
in  length,  are  placed  on  the  bottom  of  a  2  or  3  1.  flask,  and 
half  covered  with  water.  The  mouth  of  the  flask  is  then 
loosely  closed  with  a  watch-glass,  and  the  whole  allowed  to 
stand  at  the  room  temperature.  In  a  few  minutes  the  air 
inside  the  flask  will  be  found  to  be  rich  in  ozone,  which 
instantly  turns  blue  a  moistened  piece 
of  potassium  iodide  starch  paper.  As 
it  is  desirable  to  pass  the  ozonized  air 
through  certain  tubes,  the  flask  should 
be  selected  with  a  neck  small  enough 
to  be  fitted  with  a  two-holed  rubber 
stopper  which  has  two  glass  elbows 
thrust  through  it,  the  end  of  one  of 
the  elbows  extending  10  or  12  cm.  be- 
low the  bottom  of  the  stopper.  When 
water  from  the  faucet  is  allowed  to 
run  slowly  through  the  shorter  elbow, 
it  gradually  fills  the  flask,  driving  the 
ozone  out  through  the  elbow  whose 
end  is  nearest  the  bottom.  As  rubber 
rapidly  destroys  ozone,  the  ozonized  air  must  be  drawn 
from  below  the  rubber  stopper  (Fig.  14).  The  formation 
of  ozone  in  this  manner  is  dependent  on  the  temperature, 
and  at  20°  it  is  not  uncommon  to  have  very  strongly 
ozonized  air  in  the  flask  at  the  end  of  half  an  hour. 
A  large  bottle  can  be  used  instead  of  the  flask. 

Flask,  2  or  more  1.  ;  cork  and  tubes  (Fig.  14)  ;   sticks  of  P  4  cm. 
long ;  Kl-starch  paper. 


Fig.  14 


33.   From  the  slow  combustion  of  ether  in  air.  —  When 

ether  is  burned  in  air  under  certain  conditions,  a  product  is 
formed  giving  the  ozone  reactions,  and  is  commonly  called 
ozone,  though  its  nature  is  not  thoroughly  understood. 


OZONE  35 

Two  cubic  centimeters  of  ether  are  poured  into  a  200  cc. 
cylinder  and  well  shaken.  When  a  platinum  wire,  which  has 
been  heated  in  a  Bunsen  flame  and  allowed  to  cool  until  the 
glow  has  disappeared,  is  lowered  into  the  jar  containing 
the  mixture  of  ether  vapor  and  air,  a  partial  combustion 
takes  place.  A  glass  rod  heated  till  the  flame  begins  to  be 
colored  may  be  substituted  for  the  platinum  wire.  The 
gaseous  contents  of  the  cylinder  will  give  a  decided  ozone 
reaction  when  a  strip  of  iodo-starch  paper  is  introduced. 

200  cc.  cylinder  ;  platinum  wire  ;  iodo-starch  paper  ;  ether. 
PROPERTIES 

34.  Iodo-starch  paper  (potassium  iodide  and  starch). — 
Ozone  acts  upon  potassium  iodide  and  liberates  iodine.  The 
free  iodine  immediately  unites  with  the  starch,  forming  the 
blue  compound,  and  accordingly  potassium  iodide,  in  the 
presence  of  starch,  gives  an  excellent  test  for  ozone. 

One  gram  of  starch  is  suspended  in  100  cc.  of  water 
which  is  brought  to  a  boil.  After  the  starch  has  been  com- 
pletely emulsified,  .5  gram  of  potassium  iodide  is  dissolved 
in  the  solution.  Strips  of  filter  or  other  bibulous  paper  are 
dipped  in  the  solution  and  dried.  When  testing  for  ozone, 
a  strip  of  the  dried  paper  is  moistened  and  held  in  the  gas. 
The  blue  coloration  immediately  appears. 

6  KI  -f  O3  +  3  H2O  =  6  KOH  +  3  I^. 

35.  Preparation  of  ozone  paper  (potassium  iodide  and  red 
litmus). —  In  the  experiment  with  iodo-starch  paper,  in 
which  the  free  iodine  liberated  combines  with  the  starch  to 
form  the  blue  compound,  the  potassium  hydroxide  formed 
can  be  utilized  to  turn  red  litmus  paper  blue,  and  thus  serve 
as  a  delicate  test  for  ozone. 

Strips  of  blue  litmus  paper  are  dipped  in  a  solution  com- 


36  CHEMICAL  LECTURE   EXPERIMENTS 

posed  of  100  cc.  of  water,  1  drop  of  sulphuric  acid,  and  .5  g. 
of  potassium  iodide.  Red  litmus  paper  may  be  used  and 
the  sulphuric  acid  omitted.  For  preservation,  the  strips  are 
dried,  and  require  moistening  before  using.  W^hen  the  moist 
paper  is  held  in  the  presence  of  ozone,  the  color  rapidly 
turns  blue. 

36.  Action  on  mercury.  —  Ozone  acts  on  pure  mercury, 
destroying  its  lustre  and  its  mobility. 

Two  100  cc.  stoppered  cylinders,  each  containing  5  cc.  of 
pure  dry  mercury,  are  filled,  the  one  with  oxygen  and  the 
other  with  ozonized  air,  from  the  apparatus,  Fig.  14.  A 
strip  of  iodo-starch  paper  is  held  in  the  mouth  of  each 
cylinder,  and  while  it  is  unacted  upon  by  the  oxygen,  it  will 
be  immediately  turned  blue  by  the  ozonized  air.  Each  cyl- 
inder is  then  closed  and  vigorously  shaken,  when  it  will  be 
found  that  the  mercury  in  the  oxygen  cylinder  is  unacted 
upon,  while  the  mercury  in  contact  with  the  ozonized  air 
will  be  tarnished  and  will  stick  to  the  walls  of  the  vessel 
when  shaken.  That  the  ozone  has  been  destroyed  is  shown 
by  holding  a  strip  of  iodo-starch  paper  in  the  mouth  of  the 
cylinder.     Its  color  will  not  be  changed. 

Two  100  cc.  stoppered  cylinders  ;  ozonized  air  apparatus  (Fig.  14)  ; 
O  supply  ;  pure  Hg. 

37.  Oxidation  of  lead  sulphide  by  ozone.  —  The  oxidizing 
action  of  ozone  is  shown  by  its  conversion  of  the  black 
sulphide  of  lead  to  the  white  sulphate.  Lead  sulphide  is 
formed  by  moistening  a  strip  of  filter-paper  with  lead 
acetate  and  exposing  it  an  instant  to  the  fumes  of  hydrogen 
sulphide.  On  suspending  the  blackened  paper  in  a  jar  of 
ozone,  the  black  rapidly  disappears. 

38.  Decomposition  by  copper  oxide.  —  At  the  room  tem- 
perature copper  oxide  decomposes  the  ozone  molecule,  form- 
ing ordinary  oxygen. 


OZONE  37 

A  stream  of  ozonized  air  from  the  flask  (Fig.  14)  is 
passed  through  a  20  cm.  piece  of  combustion  tubing  fitted 
with  a  cork  at  each  end.  A  glass  elbow  dipping  into  a 
beaker  containing  potassium  iodide  starch  solution  is  in- 
serted in  the  cork  at  the  farther  end  of  the  combustion 
tube.  A  slow  stream  of  the  ozonized  air  is  now  passed 
through  the  system,  and  its  action  on  the  potassium  iodide 
starch  mixture  shown.  A  spiral  of  copper,  made  by  winding 
some  copper  wire  around  a  glass  rod  until  the  spiral  has 
reached  the  length  of  10  cm.,  is  then  heated  until  the  sur- 
face of  the  copper  is  entirely  oxidized.  The  cork  containing 
the  glass  elbow  is  removed,  and  the  copper  oxide  spiral, 
after  becoming  cold,  is  introduced  into  the  combustion 
tube  and  the  cork  replaced.  After  allowing  the  ozonized 
air  to  pass  through  the  system  a  few  minutes,  it  will  be 
seen  that  a  fresh  iodo-starch  solution  will  not  be  acted  upon 
by  the  gas  bubbling  through  it.  If  the  spiral  is  removed 
and  the  cork  reinserted,  the  ozonized  air  will  again  change 
the  color  of  the  solution  in  the  beaker. 

To  insure  non-contamination  of  the  iodo-starch  solution, 
two  corks  carrying  elbows  should  be  provided,  that  they,  as 
well  as  the  beakers,  may  be  changed. 

Ozonized  air  in  flask  (Fig.  14,  p.  34)  ;  20  cm.  length  combustion 
tubing ;  two  corks  carrying  glass  elbows  ;  two  50  cc.  beakers ;  iodo- 
starch  solution ;  copper  spiral. 

39.  Decomposition  by  heat.  —  Any  appreciable  increase  of 
temperature  destroys  the  ozone  molecule  and  consequently 
its  property  of  setting  free  iodine  from  potassium  iodide. 

A  gentle  stream  of  ozonized  air  from  the  flask  (Fig.  14, 
p.  34)  is  directed  through  a  5  mm.  glass  tube  connected 
at  one  end  with  an  elbow  which  dips  into  a  small  beaker 
containing  potassium  iodide-starch  solution.  On  heating 
the  glass  tube  with  a  Bunsen  burner,  the  ozone  is  destroyed 


38        '  '       qHEMICAL   LECTURE   EXPERIMENTS 

and  a  fresh  beaker  of  potassium  iodide-starch  solution  is 
unacted  upon  by  the  gas  that  bubbles  through.  A  fresh 
elbow  must  be  connected  to  the  tube. 

All  connections  should  be  made  with  glass  touching  glass, 
the  rubber  only  serving  to  hold  the  tubes  together. 

2  O3  =  3  O2. 

Ozonized  air  in  flask  (Fig.  14,  p.  34)  ;  two  glass  elbows  (5  mm.)  ; 
Kl-starch  solution. 

r 

40.  Decomposition  by  rubber.  —  The  decomposition  of 
ozone  by  rubber  and  the  consequent  necessity  of  avoiding 
rubber  connections  in  all  ozone  apparatus  is  shown  by  con- 
ducting a  rapid  stream  of  ozonized  air  through  a  1.5  m. 
length  of  rubber  tubing  and  testing  the  issuing  gas  with 
iodo-starch  paper.  The  ozonized  air  is  best  obtained  from 
the  apparatus,  Fig.  14,  p.  34,  and  the  water  should  flow 
into  the  flask  at  the  rate  of  about  40  cc.  in  10  seconds. 
The  ozonized  air  should  be  tested  just  as  it  leaves  the  glass 
elbow,  and  then  the  rubber  tube  should  be  connected. 
After  a  few  moments  the  gas  issuing  from  the  other  end  of 
the  tube  will  be  found  to  be  free  from  ozone. 

Ozonized  air  in  apparatus  (Fig.  14,  p.  34)  ;  1.5  m.  length  of 
rubber  tubing. 


HYDROGEN 


HYDROGEN 


PREPARATION 


1.  By  the  action  of  sodium  on  water.  —  Sodium  reacts 
vigorously  with  water,  liberating  hydrogen  and  forming 
sodium  hydroxide.  The  preparation  of  hydrogen  by  this 
reaction  is  only  of  theoretical  interest,  and  should  be  carried 
out  on  a  very  small  scale  only. 

A  5  mm.  piece  of  sodium  is  cut  from  a  large  piece  of  the 
fresh  metal  whose  crust  has  been  removed,  the  whole 
operation  being  performed  under  petroleum,  ether,  or  ben- 
zine. The  small  piece  is  then  freed  from  petroleum  by 
being  carefully  dried  on  a  piece  of  filter-paper.  It  is  neces- 
sary that  the  hands  should  be  dry,  as  even  small  quantities 
of  perspiration  are  liable  to  ignite  the  sodium  and  cause  a 
bad  burn.  In  case  a  bit  of  sodium  becomes  ignited,  it  can 
be  extinguished  readily  by  covering  it  with  a  handful  of 
dry  sand  (water  must  never  be  used). 

The  sodium  is  now  wrapped  in  a  piece  of  thin  sheet  lead 
(the  leaf  lining  to  tea  chests,  obtainable  at  any  grocer's, 
.serves  the  purpose  admirably),  one  end  of  the  sodium  being 
left  uncovered.  The  lead  should  be  pressed  down  on  all 
sides  closely,  and  the  end  opposite  the  exposed  end  tightly 
pinched  together.  On  dropping  the  sodium  prepared  in 
this  way  into  water  in  a  crystallizing  dish,  the  action  is 

39 


il-^^ 

— '-  — 

^ 

^ 

40        CHEMICAL  LECTURE  EXPERIMENTS 

very  gentle,  and  hydrogen  is  steadily  evolved  (Fig.  15). 

By  covering  the  sodium  with  an  inverted  jar  full  of  water, 

the   hydrogen   may   be   collected.      If    the 

sodium   is  overlapped   at  its   exposed   end 

by  the  lead,  a  bubble  of  air  often  prevents 

the  water  from  coming  in  contact  with  the 

sodium.      The  lead  should  be  trimmed  off 

just  flush  with  the  exposed  surface  of  the 

sodium.     When  tea  lead  is  used,  it  should 

be  doubled,  as  one  thickness  is  liable  to  be 

melted  through  by  the  intense  heat  of  the 
Fig.  15  &        j 

reaction.  Three  or  four  pieces  of  sodium 
may  be  wrapped  in  separate  bits  of  sheet  lead,  and  when 
the  gas  evolution  from  one  has  ceased  another  may  be 
thrown  into  the  water  and  thus  sufficient  gas  collected. 

The  wire  gauze  baskets  so  often  used  in  this  experiment 
are  liable  to  introduce  a  considerable  quantity  of  air  into 
the  gas,  with  the  possible  formation  of  an  explosive  mix- 
ture. Furthermore,  when  a  second  piece  of  sodium  is  to  be 
introduced  in  order  to  fill  a  jar  with  the  gas,  a  second  dry 
basket  must  be  used.  The  introduction  of  bits  of  sodium 
on  the  end  of  a  needle  is  not  to  be  recommended,  as  the 
metal  often  becomes  disengaged  from  the  needle  before  it  is 
under  the  jar,  and  rises  to  the  surface  of  the  water  outside, 
and  thereby  causes  annoyance. 

Sodium,  even  under  naphtha,  oxidizes  slowly,  and  while 
a  number  of  pieces  of  sodium  can  be  wrapped  in  lead  and 
preserved  in  naphtha,  the  facility  with  which  they  can  be 
prepared  leaves  very  little  to  be  gained  by  having  a  stock 
on  hand.  Freshly  prepared,  they  will  never  fail  to  give  a- 
steady  evolution  of  hydrogen. 

2  H2O  4-  2  Na  =  2  NaOH  +  H2. 

Metallic  sodium  (5  mm.  pieces)  ;  tea  lead  ;  crystallizing  dish  and 
cylinder. 


HYDROGEN 


41 


2.  From  the  reduction  of  water  vapor  by  iron.  —  Iron  acts 
upon  water  at  the  ordinary  temperatures  very  slowly.  If, 
however,  a  current  of  steam  is  conducted  over  red-hot 
metallic  iron,  the  reduction  is  very  rapid,  hydrogen  being 
liberated. 

A  60  cm.  length  of  iron  gas  pipe  is  filled  with  nails  and 
heated  to  redness  in  a  small  furnace  or  over  a  four-tube 
burner  (Fig.  16).  One  end  of  the  iron  tube  is  connected  with 
a  steam  generator  and  the  other  end  fitted  with  a  cork  and  a 
delivery-tube  leading  to  the  pneumatic  trough.  The  steam 
generator  consists  of  a  300  cc.  Erlenmeyer  flask  fitted  with  a 


Fig.  16 


two-holed  rubber  stopper,  carrying  a  long  thistle-tube  and  a 
glass  elbow  extending  to  the  combustion-tube.  The  thistle- 
tube  must  extend  to  the  bottom  of  the  flask  in  which  100 
cc.  of  water  are  brought  to  a  boil.  On  passing  a  current  of 
steam  through  the  hot  tube,  a  regular  flow  of  hydrogen  may 
be  obtained  at  the  pneumatic  trough.  Owing  to  the  conduc- 
tion of  heat  by  the  iron,  care  should  be  taken  that  the  corks 
in  the  ends  of  the  tube  are  protected  from  the  heat.  This 
can  be  accomplished  either  by  having  a  rather  long  iron 
tube  and  heating  only  the  middle  portion,  or  by  using  red 
rubber  stoppers;  which  stand  a  much  higher  temperature 
than  ordinary  cork  or  rubber  stoppers.     A  still  further  pro- 


42  CHEMICAL   LECTURE   EXPERIMENTS 

tection  may  be  secured  by  wrapping  a  thin  sheet  of  asbestos 
around  the  corks  before  inserting  them  in  the  tube.  By 
forcing  the  corks  into  the  tube,  a  tight  joint  may  be  obtained. 

60  cm.  length  gas  pipe  (1  cm.  inter,  diara.)  ;  iron  nails  ;  300  cc. 
Erlenmeyer  flask  ;  long  thistle-tube  ;  elbow  ;  4-tube  burner. 

3.  From  the  reduction  of  water  vapor  by  zinc.  —  Finely 
divided  zinc  reduces  water  vapor,  forming  zinc  oxide  and 
liberating  hydrogen.  The  temperature  at  which  the  reduc- 
tion is  effected  by  means  of  zinc  is,  however,  very  much 
lower  than  that  required  when  using  iron,  and  it  is  only 
necessary  to  heat  the  tube,  which  is  of  glass  rather  than 
of  iron,  a  little  above  the  boiling  point  of  water.  The 
apparatus  is  similar  to  that  used  in  the  preceding  experi- 
ment. The  combustion-tube  is  filled  with  zinc  dust  and 
gently  heated  with  a  four-tube  burner.  As  the  zinc  becomes 
converted  to  zinc  oxide,  a  marked  color-change  in  the  con- 
tents of  the  tube  is  noticed,  and  at  times  the  rapidity  of 
the  reduction  is  such  as  to  cause  the  zinc  to  glow. 

Zn  -f  H2O  =  ZnO  +  H2. 

Glass  combustion -tube ;  apparatus  of  preceding  experiment ;  Zn 
dust. 

4.  From  the  reduction  of  water  vapor  by  magnesium.  — 
See  Ex.  1,  p.  371. 

5.  From  the  ignition  of  sodium  hydroxide  and  iron 
powder.  —  One  gram  of  powdered  sodium  hydroxide  and  20  g. 
of  iron  powder  are  intimately  mixed  and  heated  in  a 
hard-glass  test-tube  fitted  with  a  cork  and  a  delivery-tube, 
the  upper  part  of  the  mixture  being  heated  first.  A  rapid 
stream  of  hydrogen  is  obtained,  and  the  gas  may  be 
collected  at  the  pneumatic  trough. 

Powdered  NaOH ;  Fe  powder. 


HYDROGEN  43 

6.  By  heating  calcium  hydroxide  and  zinc  dust  or  iron 
powder.  —  To  illustrate  a  technical  process  for  the  prepara- 
tion of  hydrogen,  a  mixture  of  equal  parts  by  volume  of 
zinc  dust  and  dry  calcium  hydroxide  is  heated  in  a  hard- 
glass  test-tube,  provided  with  a  cork  and  a  deli  very -tube, 
the  end  of  which  dips  into  a  pneumatic  trough.  On  apply- 
ing heat,  the  liberation  of  hydrogen  is  very  regular,  and  the 
gas  may  be  collected  in  bottles  for  testing.  It  is  important 
that  the  calcium  hydroxide  be  dry,  as  otherwise  an  excess 
of  moisture  is  likely  to  collect  on  the  tube  and  run  back, 
causing  it  to  break. 

Iron  powder  may  be  substituted  for  the  zinc  dust  in  the 
above  experiment  with  equally  satisfactory  results. 

Ca(0H)2  +  Zn  =  CaO  +  ZnO  +  H3. 

Dry  Ca(0H)2  ;  Zn  dust ;  Fe  powder. 

7.  From   aluminium  and  sodium  hydroxide  solution.— 

Fifty  cubic  centimeters  of  dilute  sodium  hydroxide  solution 
and  a  few  grams  of  scrap  aluminium  are  placed  in  a  300  cc. 
Erlenmeyer  flask  fitted  with  a  thistle-tube  and  a  delivery- 
tube.  In  the  cold  the  action  is  at  first  very  slow,  soon 
warming  up  of  itself  and  becoming  very  vigorous.  As  some 
time  is  required  for  the  reaction  to  take  place  in  the  cold, 
it  can  be  hastened  by  warming  slightly.  When  once  started 
the  flame  must  be  extinguished.  A  large  quantity  of  pure 
hydrogen  may  be  obtained  in  this  manner  from  a  very  small 
weight  of  the  metal. 

6  NaOH  -I-  2  Al  =  2  NagAlOa  +  3  R^. 

300  cc.  flask  ;  thistle-tube  ;  delivery-tube  ;  aluminium  scrap. 

8.  From  zinc  and  sulphuric  or  hydrochlpric  acid.  —  This 
method  for  the  preparation  of  hydrogen  is  almost  univer- 


44        CHEMICAL  LECTURE  EXPERIMENTS 

,  sally  used  in  the  laboratory,  by  reason  of  its  economy  and 
simplicity. 

Owing  to  its  great  importance,  large  quantities  of  hydro- 
gen are  used  on  the  lecture  table,  and  it  is  necessary  to  have 
one  or  more  forms  of  apparatus  that  will  yield  considerable 
quantities  of  the  gas. 

A  ready  supply  of  hydrogen  may  be  obtained  from  the 
apparatus  of  the  preceding  experiment.  Granulated  zinc  is 
placed  in  the  flask,  covered  with  water,  and  a  few  cubic 
centimeters  of  concentrated  sulphuric  acid  are  then  added 
through  the  thistle-tube,  which  should  extend  to  the  bottom 
of  the  flask.  After  the  addition  of  acid,  th'e  flask  and  its 
contents  are  gently  shaken.  Instead  of  adding  concentrated 
acid  to  the  water  in  the  flask,  the  acid  may  be  previously 
diluted,  and  the  cold  dilute  acid  added.  In  this  case  the 
reaction  is  not  as  rapid  at  first.  Dilute  hydrochloric  acid 
(1 : 1)  is  also  used  to  prepare  hydrogen  in  this  manner,  this 
dilution  of  acid  producing  a  rapid  gas  evolution. 

On  account  of  the  large  surface  which  is  presented  to  the 
action  of  the  acid,  the  so-called  granulated  or  feathered  zinc 
(Ex.  1,  p.  377)  is  preferred  for  making  hydrogen.  The 
diffusibility  of  hydrogen  renders  it  absolutely  essential 
that  all  apparatus  used  in  its  preparation  should  be  gas- 
tight.  Ground  glass  joints,  if  any,  should  be  well  lubricated 
with  vaseline ;  rubber  stoppers  should  be  crowded  into  place, 
and,  if  necessary,  all  connections  with  rubber  tube  should  be 
bound  with  wire. 

After  the  generation  of  the  gas  has  begun,  it  is  necessary 
to  allow  the  gas  to  escape  till  the  air  in  the  apparatus  has 
been  completely  expelled  by  the  hydrogen,  as  otherwise  con- 
siderable danger  may  result  from  the  ignition  of  an  explosive 
mixture  of  hydrogen  and  air  if  the  issuing  jet  of  hydrogen 
is  lighted  too  SQon,  According  to  the  amount  of  air  space 
in  the   generator   and  the  purifying   apparatus,  the  gas  is 


HYDHOGEN  45 

allowed  to  escape  into  the  air  for  some  time,  and  then  it  is 
better  to  test  it  before  applying  a  match  directly  to  the 
issuing  gas.  A  simple  method  of  testing  the  gas  is  to  allow 
it  to  bubble  through  a  soap  solution  contained  in  an  evap- 
orating dish  and,  after  removing  the  delivery-tube,  to  light  the 
bubbles  and  see  if  they  give  an  explosion.  If  not,  it  will  be 
safe  to  ignite  the  gas.  Another  method  is  to  lead  the  gas, 
by  means  of  a  rubber  tube,  to  the  bottom  of  an  inverted 
test-tube,  the  lighter  hydrogen  rising  and  pushing  down  the 
air  in  the  test-tube.  The  delivery-tube  is  slowly  withdrawn 
and  the  thumb  placed  over  the  mouth  of  the  test-tube,  which 
is  then  carried  to  the  Bunsen  flame  and  ignited.  When  the 
gas  is  perfectly  pure,  it  should  burn  quietly  and  give  a  flame 
of  sufficient  duration  to  serve  in  igniting  the  hydrogen 
issuing  from  the  generator.  On  the  danger  of  premature 
ignition  of  a  hydrogen  jet,  see  Exs.  29  and  30. 

Commercial  zinc  ordinarily  has  sufficient  impurity  to  give 
a  rapid  action  with  dilute  acid.  At  times,  however,  the 
zinc  may  be  so  pure  as  to  give  a  rather  slow  action.  In 
such  cases,  use  is  made  of  the  electrolytic  action  between 
zinc  and  copper  or  platinum  to  accelerate  a  liberation  of  the 
gas,  and  a  few  cubic  centimeters  of  copper  sulphate  solution, 
or  a  few  drops  of  platinic  chloride  solution,  are  added  to  the 
acid  in  the  generator.  The  zinc  becomes  coated  with  a  fine 
deposit  of  copper  or  platinum,  and  the  increased  gas  evolu- 
tion is  very  marked. 

Hydrogen  may  be  collected  either  by  displacement  of  air 
or  at  the  pneumatic  trough,  the  second  of  these  methods 
being  used  when  a  dry  cylinder  of  the  gas  is  not  required. 
In  collecting  the  gas  by  displacement  (the  operation  on  a 
small  scale  has  been  described  above),  it  is  essential  that 
a  rather  rapid  stream  of  gas  be  used,  to  prevent  the  diffusion 
of  air  into  the  vessel  to  be  filled. 

The  gas  is  dried   by  passing  it  through  a  gas  washing- 


46 


CHEMICAL  LECTURE  EXPERIMENTS 


bottle  containing  concentrated  sulphuric  acid.  When  the 
issuing  gas  is  to  be  lighted,  it  should  be  dried  by  passing 
through  a  U-tube  containing  calcium  chloride,  or  pumice- 
stone  drenched  with  sulphuric  acid.  In  either  case  the  gas 
must  have  a  clear  passageway  through  the  drier,  that  the 
flame  may  not  be  affected  by  the  irregular  bubbling  through 
a  liquid. 

If  a  special  purification  is  necessary,  the  gas  may  be  con- 
ducted through  a  gas  washing-bottle  containing  acidulated 
potassium  permanganate  solution. 

The  Kipp  generator  furnishes,  at  the  same  time,  the  most 
convenient,  as  well  as  the  most  satisfactory,  apparatus  for 
maintaining  a  constant  supply  of  hydrogen.  The  simpler 
form  of  apparatus  (Fig.  17)  consists  practically  of  two 
pieces,  the  base  being  a  glass  bottle 
constricted  in  the  middle,  forming  two 
chambers,  the  upper  chamber  being 
fitted  with  a  side  tubulature  in  which 
a  stop-cock  is  inserted,  and  the  lower 
chamber  tubulated  for  the  removal  of 
spent  acid.  The  upper  chamber  con- 
tains the  zinc,  and  the  lower  chamber 
serves  as  a  reservoir  for  gas  generated 
in  excess  of  that  wanted  for  immediate 
use.  In  the  neck  of  the  upper  chamber 
is  fitted  a  long  funnel,  the  lower  end  of 
which  extends  down  through  the  con- 
striction to  the  bottom  of  the  vessel. 
The  funnel  is  made  in  the  shape  of  a 
large  bulb  and  serves  as  an  acid  reser- 
voir. To  charge  the  apparatus,  gran- 
ulated zinc  is  introduced  through  the  opening  in  the  upper 
chamber,  and  the  stop-cock  replaced.  Dilute  hydrochloric 
acid  (1 : 1)  is  poured  into  the  funnel.      On   opening  the 


Fig.  17 


HYDROGEN  47 

stop-cock  the  acid  will  rise  in  the  lower  chamber,  pass 
through  the  constriction,  and  come  in  contact  with  the  zinc. 
The  hydrogen  generated  will  escape  through  the  stop-cock. 
When  the  stop-cock  is  closed,  the  hydrogen  presses  down- 
ward on  the  acid,  which  is  forced  back  into  the  funnel,  the 
lowest  chamber  serving  as  a  gas  reservoir.  In  order  to 
obtain  a  steady  flow  of  hydrogen,  it  is  only  necessary  to  open 
the  stop-cock. 

Zn  4-  H0SO4  =  ZnS04  +  H^. 

Zn  4-  2  HCl  =  ZnClg  -f-  H^. 

300  cc.  flask  ;  thistle  and  delivery  tubes ;  Kipp  generator  ;  HCl 
(1:1);  granulated  Zn. 

PROPERTIES 

9.  Lighter  than  air.  —  (a)  A  1  1.  beaker  is  suspended  in 
an  inverted  position  on  the  arm  of  a  lecture-balance.  The 
system  is  then  brought  into  equilibrium.  If  a  liter  cylinder 
of  hydrogen  is  inverted  under  the  mouth  of  the  beaker  and 
the  hydrogen  allowed  to  ascend,  the  equilibrium  of  the 
balance  will  be  destroyed  and  a  deflection  of  the  pointer 
be  obtained.  Instead  of  allowing  the  hydrogen  to  rise  from 
the  cylinder,  it  may  be  passed  through  a  glass  tube,  the 
mouth  of  which  will  reach  up  to  the  bottom  of  the  beaker. 
In  either  case,  however,  the  balance  must  not  be  touched 
with  the  cylinder  or  the  glass  tube. 

If  the  system  be  allowed  to  stand  for  a  few  moments,  the 
hydrogen  will  rapidly  diffuse  out,  and  the  balance  come 
again  to  equilibrium.  The  removal  of  the  hydrogen  may  be 
facilitated  either  by  unhanging  and  inverting  the  beaker  a 
moment,  or,  what  is  perhaps  more  striking,  by  sucking  out 
the  hydrogen  through  the  tube  used  to  introduce  it,  care 
being  taken,  of  course,  not  to  touch  the  beaker  or  the 
balance.     If  a  strong  suction  by  means  of  the  water-pump 


48 


CHEMICAL   LECTURE   EXPERIMENTS 


is  maintained,  the  hydrogen  will  be  rapidly  withdrawn  and 
the  balance  assume  a  state  of  equilibrium. 

Lecture-balance  ;  liter  beaker  ;  suction  pump  ;  liter  cylinder  of  H. 

(b)  The  ascending  current  of  hydrogen,  flowing  from  an 
inverted  cylinder  of  the  gas,  may  be  made  to  rotate  a  wheel 
such  as  is  described  in  Ex.  36,  p.  313. 

A  liter  cylinder  of  the  gas  inverted  under  the  buckets 
will  cause  the  wheel  to  rotate. 

Paper  wheel  (Fig  125,  p.  313)  ;  liter  cylinder  of  H. 

10.  Determination  of  the  specific  gravity.  —  By  means  of  a 
balance  weighing  two  centigrams  a  very  satisfactory  demon- 
stration of  the  fact  that  hydrogen  is  approximately  14.4 
times  lighter  than  an  equal  volume  of  air  may  be  made. 

On  one  arm  of  a  lecture-balance  a  clean,  dry,  graduated 
liter  flask  is  suspended  mouth  downwards  (Fig.  18)  by  means 
of  a  harness  of  fine  wire.     After  bringing  the  balance  into 
equilibrium  hydrogen,  dried  by  passing  through  a  gas  wash- 
ing-bottle containing  sul- 
phuric acid,  is  allowed  to 
pass  through  a  fine  tube 
into   the   inverted   flask. 
After  a  few  minutes  the 
air   will    have   been   en- 
tirely   replaced    by    the 
hydrogen,  and  it  will  be 
found  necessary  to  place 
1.14  g.  on  the  flat  bottom 
of  the  inverted  flask  in 

order  to  bring  the   sys- 
FiG.  18  .,.,  °  *: 

tem  to  equilibrium  again. 

Taking  the  weight  of  a  liter  of  air  at  the  laboratory  tem- 
perature and  standard  barometric  pressure  as  1.225  g.,  it 


HYDROGEN  49 

will  be  seen  that  the  weight  of  a  liter  of  hydrogen  is  the 
difference  between  1.225  and  1.14  or  .085  g.  On  dividing 
the  weight  of  air  under  these  conditions,  i.e.,  1.225  g.  by  the 
weight  of  an  equal  volume  of  hydrogen,  i.e.,  .085  g.,  the 
quotient  is  14.4,  or  the  air  is  14.4  times  heavier  than 
hydrogen. 

In  filling  the  flask  with  hydrogen  the  tube  should  lead 
clear  up  to  the  bottom  and  should  be  withdrawn  while  the 
gas  is  still  flowing  through  it.  If  the  graduated  flask  has  a 
long  narrow  neck,  the  rate  of  diffusion  is  so  slow  that  there 
is  no  appreciable  change  of  weight  in  bringing  the  balance 
into  equilibrium.  In  fact,  it  will  be  some  time  before  enough 
air  will  have  diffused  into  the  flask  to  disturb  the  equilibrium 
materially.  If  desirable,  a  rubber  stopper  can  be  balanced 
with  the  flask  and  inserted  after  withdrawing  the  tube 
delivering  the  hydrogen. 

Current  of  dry   H  ;   liter  graduated  flask ;    lecture-balance    and 

weights. 

11.  Use  in  balloons.  —  The  use  of  hydrogen  in  balloons 
is  shown  by  filling  a  small  collodion  balloon  with  the 
gas. 

If  a  collodion  balloon  is  obtainable,  it  is  only  necessary  to 
fasten  the  mouth  of  the  balloon  to  a  glass  tube  through  which 
hydrogen  is  passing,  and  after  the  balloon  is  completely  filled 
to  tie  the  mouth  with  a  string.  The  glass  tube  connected 
with  the  hydrogen  generator  should  be  bent  vertically  up- 
ward, contain  a  loose  2  cm.  plug  of  cotton  wool,  and  be 
drawn  down  to  a  jet  of  2  mm.  diameter.  The  end  of  the  jet 
is  rounded  a  little  in  the  flame  to  avoid  cutting  the  thin 
tissue  with  sharp  edges  of  glass.  The  collodion  balloon, 
which  should  be  flattened  as  much  as  possible  to  expel  all 
air,  is  fastened  well  up  on  the  shoulder  of  the  jet  so  that  by 
tightening  the  string  and  pushing  the  balloon  down  to  the 


50  CHEMICAL   LECTURE   EXPERIMENTS 

point  of  the  jet,  it  can  be  easily  sealed.  A  balloon  so  filled 
with  hydrogen  rises  in  the  air  and  will  support  a  con- 
siderable length  of  string  or  thread  which  may  be  used 
to  recover  it. 

H  generator  ;  collodion  balloon  ;  glass  jet  with  cotton  thread. 

12.  Filling  a  balloon  under  pressure.  —  (a)  The  collodion 
balloons  used  in  the  preceding  experiment  are  short  lived 
and  somewhat  expensive.  The  small  thin  rubber  bags  so 
often  used  on  toy  whistles  or  in  games  ^  are  admirably 
adapted  for  experimenting  with  hydrogen,  if  provision  is 
made  to  fill  them  with  the  gas  under  pressure,  since  it  is 
necessary  to  fill  not  only  the  small  volume  of  the  rubber 
bag,  but  to  cause  its  distension  and  thereby  enclose  a  con- 
siderable quantity  of  gas.  The  apparatus  for  conducting 
the  hydrogen  into  the  rubber  bag  consists  of  a  1  or  2  1. 
bottle  having  a  two-holed  rubber  stopper  carrying  an  elbow 
and  a  jet  such  as  is  described  in  the  preced- 
ing experiment  (Fig.  19).  The  bottle  is  first 
filled  with  hydrogen  either  over  water  or  by 
displacement,  and  the  stopper  inserted,  care 
being  taken  to  allow  no  hydrogen  to  escape. 
A  rubber  tube  connects  the  water  tap  with 
the  glass  elbow.  The  rubber  bag  is  securely 
fastened  on  the  shoulder  of  the  jet  as  de- 
scribed in  the  preceding  experiment.  By 
allowinor  the  water  to  flow  into  the  bottle, 


Fig.  19 

the  gas  is  forced  under  considerable  pressure 

out  through  the  jet  into  the  rubber  bag,  which  may  be  dis- 
tended and  form  a  balloon  some  15  cm.  in  diameter. 

H    generator ;   2   1.    bottle ;    2-holed  stopper ;    elbow ;    jet ;   thin 
rubber  bag. 

1  Rubber  bags  of  this  form  may  be  obtained  at  any  toy  store. 


HYDROGEN 


51 


(b)  If  the  hydrogen  generator  is  so  constructed  as  to 
permit  of  considerable  pressure,  the  gas  may  be  drawn 
directly  from  the  generator  into  the  rubber  balloon.  A  thick- 
walled  flask  is  provided  with  a  two-holed  cork  carrying  a 
small  long-stemmed  dropping-funnel  and  one  arm  of  a  three- 
way  stop-cock  (Fig.  20).  The  zinc  is  placed  in  the  flask  and 
dilute  hydrochloric  acid  (1 : 1)  al- 
lowed to  flow  through  the  drop- 
ping-funnel into  the  flask.  The 
three-way  stop-cock  should  be  so 
arranged  that  the  gas  escapes 
through  the  open  arm  of  the  T. 
The  rubber  balloon  is  tied  to  a 
jet  (such  as  is  described  in  the 
preceding  experiments)  which  is 
connected  by  means  of  a  short 
piece  of  rubber  tubing  to  the 
stem  of  the  T-tube.  When  all 
the  air  has  been  driven  out  of 
the  generator,  the  three-way  stop- 
cock  should  be  turned  so  as  to 

deliver  hydrogen  through  the  stem  of  the  T  into  the  balloon. 
It  is  necessary  to  close  the  stop-cock  on  the  dropping-funnel 
immediately,  as  otherwise  the  gas  will  push  up  through  the 
column  of  liquid  and  out  through  the  funnel.  When  the 
rubber  has  been  distended  to  a  sufficient  size,  the  three-way 
cock  may  be  so  turned  as  to  seal  the  stem  of  the  T-tube  and 
open  both  arms,  allowing  a  vent  for  the  compressed  gas 
inside  the  generator.  The  balloon  may  then  be  tied  and 
drawn  off  the  jet  as  described  in  the  preceding  experiment. 
If  proper  care  is  used  in  opening  and  closing  the  stop-cock, 
this  method  of  filling  a  rubber  balloon  leaves  very  little  to 
be  desired. 


Fig.  20 


Stout-walled   flask  ;    dropping-funnel 
balloon. 


three-way    cock  ;    rubber 


52       CHEMICAL  LECTURE  EXPERIMENTS 

13.  Soap-bubbles  blown  with  hydrogen. — If  soap-bub- 
bles are  tilled  with  hydrogen,  they  will  rise  rapidly  and,  if 
touched  with  a  lighted  taper,  burn. 

Hydrogen  from  a  Kipp  generator  is  first  passed  through 
a  U-tube  containing  soda-lime  slightly  moistened,  i.e.,  not 
dry  enough  to  have  any  dust,  and  then  through  a  rubber 
tube  connected  with  an  ordinary  thistle-tube.  The  soda- 
lime  tube  completely  removes  any  hydrochloric  acid  vapor, 
which  is  quite  destructive  to  the  soap  film.  After  dipping 
the  mouth  of  the  thistle-tube  in  the  soap  solution^  and 
shaking  off  the  excess  of  water,  the  bubble  is  started  with 
the  mouth  of  the  thistle-tube  downwards.  When  the 
bubble  has  attained  the  size  of  the  thistle,  the  mouth  may 
be  pointed  upwards  and  the  hydrogen  admitted  as  fast  as 
desired.  By  means  of  the  glass  stop-cock  in  the  Kipp  gener- 
ator the  supply  of  hydrogen  may  be  easily  regulated.  On 
giving  the  tube  a  little  side  shake,  the  bubble  is  released 
and  immediately  ascends.  A  small  taper  or  candle  fastened 
on  the  end  of  a  long  stick  may  be  used  to  ignite  the  bubble, 
and  it  is  better  to  hold  the  flame  above  the 
^  '^Ht^  bubble,  bringing  it  down  so  as  to  meet  it,  rather 
/  N  than  to  try  to  follow  the  bubbles  and  catch  them 
as  they  ascend. 

A  glass  or  preferably  tin  funnel  15  cm.  across 
the  top  (Fig.  21)  may  be  clamped  mouth  down- 
wards to  the  gas  pipe  or  other  fixture  over  the 
lecture-table,  and  a  small  gas-jet  burning  at  the 
end  of  a  glass  tip  may  be  so  arranged  that  it 
will  burn  horizontally  across  the  mouth  of  the 
Fig.  21       funnel.     If  the  hydrogen  bubbles  are  allowed 

1  Preparation  of  soap  solution. — The  presence  of  glycerine  in  soap 
solution  used  in  blowing  soap-bubbles  materially  increases  the  dura- 
bility of  the  film. 

One  hundred  grams  of  white  castile  (or  any  other  pure  soap)  are 


HYDROGEN 


63 


to  rise  beneath  this  funnel,  they  will  ascend  and  come  in 
contact  with  the  gas  flame,  insuring  ignition.  The  mouth 
of  the  funnel  should  be  about  1.5  m.  from  the  point  of 
liberation  of  the  bubble. 

H  generator  (Kipp)  ;  candle  at  the  end  of  a  long  stick  ;  thistle- 
tube  ;  soap  solution  ;  soda-lime  ;  U-tube. 


14.  Conductivity  for  heat.  —  Hydrogen,  in  contrast  to 
the  other  gases,  is  a  good  conductor  of  heat,  and  this  prop- 
erty, which  it  shares  in  common  with  the  metals,  is  well 
shown  by  lowering  a  jar  of  hydrogen  over  a  piece  of  platinum 
wire  which  has  been  heated  by  means  of  the  electric  current. 

A  20  mm.  piece  of  fine  platinum  wire  is  connected  with 
two  upright  copper  wires  fastened  to  a  small  block  of  wood. 
The  copper  wires  should  be  30  cm.  long 
and  so  arranged  that  about  a  20  cm. 
length  stands  upright  from  the  board. 
They  are  fastened  about  25  mm.  apart, 
thus  permitting  the  lowering  of  the  cyl- 
inder of  hydrogen  over  them  (Fig.  22). 
The  copper  wires  are  connected  with  a 
battery  of  sufficient  strength  to  just  raise 
the  platinum  wire  to  incandescence.  On 
lowering  the  jar  of  hydrogen  over  the 
glowing  wire  the  gas  will  be  ignited  at 
the  mouth  of  the  jar,  and  the  glow  will 
nearly  if  not  entirely  disappear  from  the 
wire.  On  removing  the  jar,  the  glow 
will  again  appear. 


n 

^ 

r,.     ...q 

Fig.  22 


cut  in  thin  shavings  and  placed  in  a  bottle  with  1  1.  of  water.  The 
mixture  should  be  well  shaken  until  a  saturated  solution  of  soap  is 
obtained.  After  allowing  the  liquid  to  stand  for  some  time  the  clear 
supernatant  solution  is  decanted  and  mixed  with  half  its  volume  of 
glycerine. 


54  CHEMICAL   LECTURE  EXPERIMENTS 

The  strength  of  the  current  may  be  previously  determined 
and  the  jar  lowered  before  the  connections  are  made.  On 
switching  on  the  current,  the  wire  will  undergo  no  apparent 
change,  but  on  withdrawing  the  jar,  it  will  become  heated 
and  ignite  the  hydrogen  at  the  mouth  of  the  cylinder.  The 
platinum  wire  should  be  as  line  as  possible  (such  as  that 
used  in  suspending  Welsbach  mantles),  and  care  should  be 
taken  not  to  have  the  current  strong  enough  to  melt  it. 

Fine  iron  wire  may  be  used  in  place  of  platinum,  though 
it  cannot  be  raised  to  as  high  a  degree  of  incandescence 
without  danger  of  oxidation  and  combustion  in  air.  In  this 
case  it  is  better  to  lower  the  jar  and  then  close  the  circuit 
and  allow  the  iron  wire  to  become  heated  on  removing  the 
jar  containing  hydrogen. 

Fine  platinum  or  iron  wire ;  stout  copper  wire  ;  battery ;  jar  of 
hydrogen. 

15.  Non-conductivity  for  sound.  —  Hydrogen  is  a  poor 
conductor  of  sound,  and  consequently  when  a  bell  is  thrust 
into  an  atmosphere  of  hydrogen  and  then  struck,  very  little 
if  any  sound  is  heard. 

A  small  bell  is  fastened  on  the  end  of  a  stick  or  wire  and 
then  thrust  up  into  a  liter  bell-jar  of  hydrogen.     If  the  bell 
r-%  is  then  struck  with  a  second  piece  of  wire  or 

f^          \     a  file,  the  sound  is  very  much  diminished. 

The  effect  is  more  striking  if  an  electric  bell 
(Fig.  23)  is  used.  A  switch  should  be  placed  in 
the  circuit,  which  is  closed  after  the  bell  is  thrust 
into  the  jar.  The  box  which  usually  covers  the 
magnets  of  the  bell  should  be  removed,  as  it  is 
possible  to  have  an  explosive  mixture  of  hydro- 
gen  and  air  formed  inside  the  box  which  might 
be  ignited  by  the  feeble  spark  produced  at  the  contact. 

Two  1  liter  bell-jars ;  bell  and  wire  ;  electric  bell ;  battery  and 
switch ;  H  generator, 


HYDROGEN 


55 


16.   Diffusibility.  —  The   great   diffusibility  of  hydrogen 
through  the  walls  of   a  porous  cell  may  be  shown  by  a 
number  of  striking  experiments  in  which  the  variations  in 
pressure  caused  by  the  hydrogen  enter- 
ing or  leaving  the  cell  are  utilized. 

A  porous  cell,  approximately  12  cm. 
long  and  5  cm.  in  diameter,  is  provided 
with  a  two-holed  rubber  stopper  tightly 
fitted  into  its  mouth.  Through  one  hole 
a  5  cm.  length  of  glass  tubing  of  6  mm. 
internal  diameter  is  thrust,  and  through 
the  other  a  short  piece  of  small  glass 
tubing  about  3  mm.  internal  diameter. 
The  smaller  glass  tube  is  plugged  with 
a  short  piece  of  rubber  tubing  and  a  bit 
of  glass  rod.  The  larger  tube  is  con- 
nected by  means  of  a  rubber  tube  with  a 
long  glass  U-tube  half  filled  with  colored 
water.  If  a  jar  of  hydrogen  is  now 
brought  down  over  the  porous  cell,  the 
pressure  inside  is  increased  and  the  level  of  the  water  in 
the  U-tube  will  be  disturbed,  that  in  the  arm  connected 
with  the  porous  cell  falling,  that  in  the  other  arm  rising  an 
equal  distance. 

Porous  cup  ;  long  glass  U-tube  ;  ink  water  ;  jar  of  H. 


Fig.  24 


17.  Diffusion  out  of  a  porous  cup.  — When  the  interior  of 
the  porous  cup  is  filled  with  hydrogen,  the  diffusion  out- 
ward is  so  rapid  as  to  cause  an  internal  diminution  of 
pressure. 

The  jet  tube  is  removed  from  the  Wolff  bottle  in  Fig.  25 
and  a  rapid  stream  of  hydrogen  is  sent  into  the  porous  cup 
through  a  small  glass  tube  which  is  provided  with  a  rubber 
connector  and  a  pinch-cock.     On   suddenly   stopping  the 


56 


CHEMICAL  LECTURE  EXPERIMENTS 


flow  of  the  gas  by  closing  the  pinch-cock,  the  hydrogen  will 
diffuse  out  of  the  porous  cup  into  the  air,  diminishing  the 
internal  pressure  inside  the  cup.     The  colored  water  will 
rise  immediately  in  the  pipette,  nearly  filling  the  bulb. 
Apparatus  (Fig.  25)  ;  H  generator  (Kipp). 

18.  Diffusion  producing  a  fountain.  —  One  neck  of  a 
small  two-necked  Wolff  bottle  is  fitted  with  a  glass  tube 

whose  lower  end  nearly  touches  the  bot- 
tom of  the  bottle,  the  upper  end  reach- 
ing a  few  centimeters  through  the  cork 
and  being  drawn  down  to  a  fine  jet 
(Fig.  25).  The  Wolff  bottle  is  then 
nearly  filled  with  water  colored  with 
ink.  The  stem  of  a  100  cc.  pipette  is 
thrust  through  a  rubber  stopper  in  the 
second  neck,  extending  nearly  to  the 
bottom  of  the  bottle.  The  upper  end 
of  the  pipette  is  connected  with  the 
porous  cell  described  in  Ex.  16.  On 
lowering  a  bell-jar  of  hydrogen  over 
the.  porous  cell,  the  internal  pressure 
becomes  so  great  that  the  water  is 
forced  out  of  the  Wolff  bottle  in  a 
fine  jet  to  a  considerable  height. 

Apparatus  (Fig.  25)  ;  2-necked  500  cc.  Wolff  bottle  ;  100  cc. 
pipette  ;  porous  cup  used  in  Ex.  16  ;  glass  jet  to  fit  second  neck  of 
the  Wolff  bottle  ;  bell-jar  of  H. 

19.  Diffusion  and  its  application  to  the  fire-damp  indi- 
cator. —  The  porous  cup  in  Ex.  16  is  connected  with  one 
limb  of  a  U-tube  which  is  half  filled  with  mercury.  Through 
the  open  end  of  the  U-tube  two  insulated  annunciator  wires 
twisted  together  are  thrust,  the  ends  of  which  are  made 
bare  so  as  to  give  good  electrical  contact.     One  of  the  wireg 


Fia.  25 


HYDKOGEN 


57 


Fig.  26 


dips  some  distance  into  the  mercury,  and  the  bare  end  of 
the  other  wire  is  held  a  millimeter  above  the  mercury  menis- 
cus. On  lowering  the  bell-jar  of  hydro- 
gen over  the  porous  cup,  the  internal 
pressure  will  cause  the  mercury  in  the 
open  end  of  the  U-tube  to  rise,  thereby 
closing  an  electric  circuit,  which  con- 
sists of  a  battery  and  a  bell  ^  or  buzzer. 

The  practical  application  of  the  indi- 
cator in  mines  may  be  better  shown  by 
having  the  bell  at  some  distance  from 
the  lecture  table ;  in  the  back  part  of  the 
room,  for  example.  A  further  realism 
may  be  added  by  covering  the  apparatus 
with  a  large  box  or  closet  and  admitting  illuminating  gas 
into  its  interior,  thereby  creating  an  artificial  fire-damp. 

Porous  cup  used  in  Ex.   16 ;    insulated  annun- 
ciator wire  ;  battery  ;  bell  or  buzzer  ;  U-tube  ;  Hg, 


20.  Diffusion  through  rubber.  —  That 
hydrogen  also  readily  diffuses  through  a 
material  such  as  rubber  may  be  shown 
by  means  of  the  following  apparatus  (Fig. 
27) :  — 

A  tubulated  bell-jar  is  fitted  with  a  cork 
and  a  wide  glass  tube  20  cm.  long.  A  piece 
of  thin  dentist's  rubber  is  tightly  stretched 
over  the  mouth  of  the  jar,  and  tightly  tied 
on  with  a  string  passing  under  the  rim  of 
glass  around  the  mouth  of  the  jar.  After 
clamping  the  apparatus  in  an  upright  posi- 
tion, hydrogen  is  conducted  through  a  fine 


Fig.  27 


1  Dry  batteries  and  bells  or  annunciators  or  buzzers  are  readily  ob- 
tainable at  almost  any  electrical  supply  store,  at  a  very  low  price. 


58 


CHEMICAL   LECTURE   EXPERIMENTS 


tube  small  enough  to  be  pushed  up  through  the  larger  tube 
into  the  bell-jar.  When  all  the  air  is  displaced,  the  small 
glass  tube  is  withdrawn  without  stopping  the  flow  of  hydro- 
gen, and  a  vessel  of  colored  water  is  so  placed  that  the  large 
glass  tube  will  dip  under  the  surface  of  the  water.  Soon 
the  hydrogen  will  begin  to  diffuse  out  through  the  rubber, 
and  the  colored  water  will  rise  in  the  glass  tube. 

Apparatus  (Fig.  27)  :   small  tubulated  bell-jar ;   sheet  of  dentist's 
rubber  15  cm.  square  ;  ink  water. 

21.   Separation  of  hydrogen  and  oxygen  by  diffusion.— 

The  elements  of  oxyhydrogen  gas  may  be  separated  by 
diffusion  by  passing  a  slow  stream  of  the  gas  through  a 
long  porous  tube  and  testing  the  gas  issuing  at  the  other 
end  after  collecting  it  over  water.  The  hydrogen  being 
much  more  diffusible  than  oxygen,  rapidly  passes  out 
through  the  walls  of  the  porous  tube,  leaving  the  oxygen 
behind. 

A  simple  apparatus  for  demonstrating  this  principle  may 
be  made   by  connecting  the  tips  of  two  clay  pipes  w|th 

extra  long  stems  by  a 
short  piece  of  rubber  tub- 
ing. The  bowl  of  each 
pipe  is  closed  with  a  one- 
holed  rubber  stopper.  One 
pipe  is  connected  with  a 
supply     of     oxyhydrogen 


gas, 


and   the   other   with 


a  pneumatic  trough  (Fig. 

28).  The  rate  at  which 
Pjq  28  t^^    gaseous    mixture    is 

passed  through  the  pipes 
will  influence  in  a  marked  degree  the  composition  of  the 
gas  collected  at  the  pneumatic  trough.     If  the  rate  is  too 


HYDROGEN  59 

rapid,  the  hydrogen  will  not  have  time  to  diffuse  out, 
and  the  collected  gas  will  still  retain  its  explosive  char- 
acter. If  the  rate  is  too  slow,  sufficient  air  to  dilute  the 
oxygen  will  have  diffused  into  the  tube,  and  the  collected 
gas  will  not  relight  a  glowing  splinter.  A  preliminary  test 
should  be  made  to  determine  the  rate  of  bubbling  in  the 
pneumatic  trough  that  will  give  the  most  satisfactory 
results.  For  preliminary  testing  not  more  than  30  cc. 
should  be  collected  at  one  time.  The  so-called  church- 
warden pipes  serve  this  purpose  admirably,  and  they  may 
be  mounted  in  a  double  burette  clamp.  The  oxyhydrogen 
gas  is  best  held  in  a  tubulated  bell-jar  fitted  with  a  cork 
and  a  stop-cock,  immersed  in  a  pail  of  water.  The  jar  is 
filled  one-third  with  oxygen  and  two-thirds  with  hydrogen. 
The  effect  of  increasing  and  diminishing  the  rate  of  flow 
of  the  gases  should  be  noticed  after  the  experiment  is 
ended.  Increasing  the  flow  causes  the  collected  gas  to 
explode;  diminishing  the  flow  contaminates  the  collected 
gas  with  air  to  such  an  extent  that  a  glowing  splinter  is 
not  rekindled. 

Oxyhydrogen  gas  in  a  tubulated  bell-jar  ;  2  churchwarden  pipes  ; 
double  burette  clamp. 

22.  Combustion  in  air.  —  (a)  The  characteristic  colorless 
hydrogen  flame  is  best  obtained  by  allowing  gas  from  a 
Kipp  generator  (free  from  air)  to  burn  at  the  tip  of  an 
ordinary  blowpipe.  The  flame  is  so  nearly  colorless  that  it 
cannot  be  seen  at  a  distance,  so  its  presence  is  shown  by 
igniting  a  piece  of  paper  with  it  or  by  holding  in  it  a  fine  piece 
of  platinum  wire,  which  will  be  heated  to  incandescence. 

In  case  a  glass  jet  is  used,  the  flame  will  be  colored  yel- 
low from  the  sodium  in  the  glass.  A  platinum  tip  (Ex. 
5,  p.  182)  may  be  substituted  for  the  glass  or  blowpipe  jet. 

Blowpipe  jet ;  fine  platinum  wire. 


60 


CHEMICAL  LECTURE   EXPERIMENTS 


^^^ 


Fig.  29 


(&)  Owing  to  its  low  specific  gravity,  hydrogen  may  be 
siphoned  out  of  a  glass  bell- jar  by  means  of  a  glass  siphon 
tube,  8  to  10  mm.  in  diameter.  A  large  bell-jar  is  clamped 
mouth  downwards  and  the  shorter  limb  of  a  glass  siphon 
thrust  up  into  it  (Fig.  29).  A  rapid  stream 
of  hydrogen  from  a  generator  enters  the  bell- 
jar  through  the  siphon  tube,  pushing  the  air 
down  until  the  jar  is  completely  filled  with 
hydrogen.  The  rubber  tube  leading  from  the 
generator  is  disconnected,  and  the  hydrogen 
begins  to  flow  upwards  out  of  the  longer  arm 
of  the  siphon.  After  the  siphon  is  started, 
the  gas  may  be  lighted  at  the  upper  end,  and 
will  burn  quietly  until  the  mixture  of  air  and 
hydrogen  reaches  the  flame,  when  the  latter 
will  be  seen  to  run  slowly  back  through  the  siphon,  igniting 
the  explosive  gaseous  mixture  inside  the  bell-jar, 
producing  a  loud  though  harmless  report. 

Apparatus  (Fig.  29)  ;  large  bell-jar  ;  siphon  tube  (1  cm. 
inter,  diara.). 

23.  Chemical  harmonica.  —  Hydrogen  is  ig- 
nited at  the  end  of  a  metal  blowpipe  tip,  which 
is  straightened  out  and  clamped  in  a  vertical 
position,  and  glass  tubes  of  varying  diameters 
are  lowered  in  turn  some  15  cm.  over  the  burn- 
ing jet  (Fig.  30).  As  the  flame  burns  in  the 
glass  tubes,  it  produces  wave  motions  resulting 
in  different  tones.  By  varying  the  diameters  of 
the  glass  tubes  and  the  distance  that  they  are 
lowered  over  the  burning  jet,  great  diversity  in 
tone  may  be  produced.  The  glass  tubes  should 
not  be  too  small  in  diameter.  As  a  general  rule  the  maxi- 
mum diameter  giving  satisfactory  results  is  equal  to  the 


/ 


Fig.  30 


HYDROGEN  61 

length  of  the  hydrogen  flame ;  so  a  flame  2  cm.  long  would 
give  a  tone  with  a  glass  tube  2  cm.  in  diameter. 
Straight  metal  blowpipe  ;  glass  tubes,  different  sizes. 

24.  Ignition  of  hydrogen  by  platinized  asbestos.  —  (a)  A 

stream  of  hydrogen  impinging  on  finely  divided  platinum  is 
ignited. 

A  small  bundle  of  asbestos  fibre  is  wound  in  a  loop  at  the 
end  of  a  stout  copper  wire  and  moistened  with  a  few  drops 
of  platinum  chloride  solution.  On  ignition  in  a  Bunsen 
flame  the  platinum  chloride  is  decomposed  and  the  asbestos 
coated  with  a  fine  deposit  of  metallic  platinum.  On  cooling 
and  holding  the  platinized  asbestos  in  a  stream  of  hydrogen, 
it  is  first  seen  to  glow,  and  then  almost  instantaneously  the 
hydrogen  is  ignited.  This  is  the  principle  of  the  self- 
lighting  lamp  of  Dorbereiner. 

Asbestos  ;  copper  wire  ;  platinum  chloride  solution. 

(b)  A  dry  jar  is  filled  with  hydrogen  by  displacement  and 
held  in  a  slightly  inclined  position  mouth  downwards.  On 
carefully  introducing  the  bundle  of  platinized  asbestos  near 
the  mouth  of  the  jar,  it  will  be  seen  that  the  asbestos  will 
glow,  causing  a  combustion  of  the  hydrogen.  If  now  the 
asbestos  is  carefully  inserted  into  another  dry  jar  of  hydro- 
gen, its  introduction  can  be  so  regulated  that  the  combustion 
of  the  hydrogen  and  the  air  will  not  be  produced  on  the 
asbestos  to  such  an  extent  as  to  cause  the  ignition  of  the 
hydrogen.  The  water  formed  by  this  slow  combustion  will 
be  seen  as  white  clouds  at  the  mouth  of  the  jar,  which  finally 
condense  as  moisture  on  the  walls  of  the  cylinder.  If  the 
bundle  of  asbestos  is  suddenly  thrust  up  the  jar  into  the 
hydrogen  atmosphere,  it  will  no  longer  glow,  and  the  action 
ceases.  On  withdrawing  it  till  it  comes  in  contact  with  the 
zone  between  the  hydrogen  and  the  air,  the  combustion  again 
proceeds. 

Two  200  cc.  dry  cylinders  of  hydrogen  ;  platinized  asbestos. 


62L  CHEMICAL   LECTURE   EXPERIMENTS 

25.  Reduction  of  cupric  oxide  by  hydrogen.  —  A  small 
quantity  of  powdered  cupric  oxide  is  placed  on  a  porcelain 
crucible  lid,  the  ring  of  which  is  pressed  into  a  slit  in  a 
cork  fastened  on  the  end  of  a  long  iron  wire.  This  arrange- 
ment permits  of  thrusting  the  crucible  lid  up  into  an  atmos- 
phere of  hydrogen  in  a  dry  liter  cylinder.  The  cylinder  is 
first  filled  with  hydrogen  and  clamped  in  a  vertical  position 
with  the  mouth  downwards,  the  mouth  being  kept  closed  by 
holding  a  glass  plate  against  it.  The  cupric  oxide  is  heated 
from  above  with  a  small  Bunsen  flame  till  quite  hot  and 
then  thrust  rapidly  up  into  the  hydrogen.  Soon  moisture 
condenses  on  the  side  of  the  jar,  and  on  allowing  the  cupric 
oxide  to  cool  in  the  atmosphere  of  hydrogen  for  a  few 
minutes  and  then  withdrawing  it,  it  will  be  seen  to  have  the 
characteristic  red  color  of  metallic  copper. 

Crucible  lid  ;  cork  ;  stout  iron  wire ;  liter  cylinder  of  H ;  CuO 
powder. 

OXYHYDROGEN    GAS   AND   WATER 

26.  Formation  of  water  by  the  combustion  of  hydrogen  in 
air.  —  (a)  By  passing  the  products  of  combustion  of  hydrogen 
in  air  through  a  U-tube,  a  considerable  quantity  of  water  is 

condensed  in  a  short  time.    In  the 
apparatus   (Fig.  31)  one   limb  of 
-■ — ^        ^  n    the  U-tube  is  fitted  with  a  rubber 

f=l    f-4  II    stopper   and   a   glass    elbow   con- 

nected   with    the     suction -pump. 
The  other  limb   is   fitted  with  a 
cork  containing  the  small  end  of 
a  bent    thistle-tube.       Hydrogen, 
dried  by  passing  through  a  U-tube 
containing  calcium  chloride,  is  allowed  to  burn  from  a  blow- 
pipe jet  held  immediately  under  the  bulb  of  the  thistle-tube. 
The  rate  of  suction  must  not  be  such  as  to  cause  the  first 


OXYHYDROGEN    GAS   AND   WATER  63 

limb  of  the  U-tube  to  become  warm  enough  to  vaporize  ^ny 
water  that  may  have  condensed. 

Apparatus  (Fig.  31);  U-tube;  bent  thistle-tube  ;  metallic  blowpipe 
jet ;  CaClg  drying  tube. 

(b)  Dry  hydrogen  is  allowed  to  escape  through  a  blow- 
pipe jet  and  a  dry  liter  bell-jar  is  held  over  the  tip  to  show 
that  no  moisture  is  deposited  inside  the  jar.  On  lighting 
the  hydrogen  jet  and  bringing  the  bell-jar  again  over  the 
flame,  moisture  will  soon  be  deposited  all  over  the  inside  of 
the  jar.  The  hydrogen  flame  should  not  be  high  enough  to 
generate  sufficient  heat  to  break  the  jar. 

H  generator  ;  drying  tube  ;  blowpipe  jet  ;  liter  bell-jar  (dry). 

27.  Synthesis  of  water  by  reduction  of  cupric  oxide  by 
hydrogen.  —  A  hard-glass  bulb-tube  may  be  packed  full  of 
cupric  oxide,  such  as  is  used  in  elementary  organic  analysis, 
and  weighed.  After  reduction  and  cooling  in  a  current  of 
hydrogen,  the  loss  in  weight  may  very  readily  be  noted. 
The  water  formed  may  be  collected  in  a  U-tube  containing 
glass  beads  or  bits  of  pumice-stone  drenched  with  concen- 
trated sulphuric  acid.  A  U-tube  containing  10  g.  of  sulphuric 
acid  will  take  up  approximately  1  g.  of  water,  though,  if  a 
U-tube  having  a  bulb  blown  on  one  arm  is  used,  the  greater 
portion  of  the  water  will  condense  in  the  bulb  and  the  sul- 
phuric acid  will  absorb  the  uncondensed  moisture.  In  this 
way  several  grams  of  water  may  be  collected  with  quantita- 
tive accuracy.  With  careful  manipulation  it  is  not  a  dif- 
ficult matter  to  make  the  whole  experiment  quantitative,  i.e., 
to  determine  the  loss  of  weight  of  the  cupric  oxide  and  the 
weight  of  water  formed.  With  these  data  a  simple  calculation 
will  show  that  8  parts  of  oxygen  require  1  part  of  hydrogen 

to  form  water. 

CuO  +  H2  =  Cu  H-  H2O. 

Hard-glass  bulb-tube  ;  H2SO4  and  pumice-stone  U-tube  ;  current 
of  purified  H  ;  granular  CuO. 


64  CHEMICAL  LECTURE   EXPERIMENTS 

28.  The  oxyhydrogen  flame.  —  The  intense  heat  of  hy- 
drogen burning  in  air  may  be  still  more  increased  by 
introducing  a  jet  of  burning  oxygen  in  the  centre  of  the 
hydrogen  flame.  The  hydrogen  burning  under  these  condi- 
tions is  furnished  with  a  supply  of  oxygen  from  the  air  on 
the  outside  and  pure  oxygen  for  the  interior,  giving  rise  to 
the  intensely  hot  oxyhydrogen  flame.  In  burning  these  two 
gases  a  special  form  of  burner  is  required,  consisting  essen- 
tially of  a  tube  in  the  centre  of  which  a  fine  jet  is  longi- 
tudinally placed.  Hydrogen  is  admitted  to  the  larger  tube 
and  ignited  at  its  mouth.  A  gentle  current  of  oxygen  is 
then  directed  through  the  fine  jet  into  the  centre  of  the 
hydrogen  flame.  Burners  specially  adapted  for  this  form 
of  flame  are  much  used  in  producing  the  so-called  calcium 
or  Drummond  light. 

In  case  such  a  burner  is  not  obtainable  the  phenomenon 
may  be  studied,  though  less  advantageously,  with  an  ordi- 
nary gas  blast-lamp.  Unless  a  large  hydrogen  generator  is 
at  hand,  it  is  more  satisfactory  to  use  illuminating  gas 
in  place  of  hydrogen.  Oxygen  may  be  obtained  from  a 
gasometer  or  from  a  steel  cylinder.  In  using  the  lamp, 
illuminating  gas  is  first  admitted  to  the  larger  tube  and 
ignited  at  the  mouth  of  the  burner,  where  it  will  burn  with 
a  flickering,  smoky  flame.  Oxygen  is  then  gradually  admit- 
ted through  the  central  air  tube.  As  the  result  of  the 
increase  in  temperature,  the  illuminating  gas  burns  with 
almost  dazzling  brilliancy,  which  gradually  diminishes  as 
more  oxygen  is  admitted.  The  heat  is  so  great  that  only  a 
small  flame,  some  5  or  6  cm.  in  length,  can  be  used.  Hydro- 
gen or  coal  gas  under  considerable  pressure,  when  used  with 
a  regular  oxyhydrogen  burner,  will,  however,  give  flames  of 
any  desired  length.  The  small  colorless  pointed  flame  is 
extremely  hot,  and  may  be  used  in  any  of  the  following 
experiments  to  show  its  intense  heat. 


OXYHYDROGEN    GAS   AND    WATER  65 

A  bundle  of  iron  wires  or  a  small  rat-tail  file,  when  held 
in  the  flame,  burns  with  great  brilliancy,  sending  out  show- 
ers of  sparks.  The  molten  globules  of  iron  oxide  fall  to 
the  table,  which  should  be  protected  with  a  sheet  of  asbestos 
paper.  The  burner  should  be  so  placed  that  the  flame  is 
horizontal.  After  the  iron  has  become  well  ignited,  the 
illuminating  gas  may  be  cut  off  and  the  iron  held  in  the  jet 
of  oxygen,  where  it  continues  to  burn. 

A  thick  copper  wire  is  immediately  melted  when  held  in 
the  flame. 

Pieces  of  zinc,  lead,  and  cadmium  are  readily  oxidized, 
while  silver,  though  not  oxidized,  is  soon  melted  to  a  bright 
metallic  globule,  which  by  continued  heating,  may  be  made 
to  boil.  The  silver  should  be  placed  in  a  small  bone-ash 
cupel  and  the  flame  directed  upon  it  from  above.  If  after 
the  silver  is  melted  it  is  allowed  to  cool  in  a  current  of 
oxygen,  a  considerable  quantity  of  the  gas  will  be  absorbed 
by  the  metal,  and  just  before  solidification  the  gas  will 
be  given  off  suddenly,  causing  a  spurting  out  of  the 
metal. 

A  piece  of  thick  platinum  wire  held  in  the  flame  is  soon 
melted  to  a  globule,  which  may  be  shaken  from  the  wire  and 
allowed  to  drop  into  a  dish  of  water  placed  beneath  the 
flame. 

A  glass  rod  held  in  the  flame  is  immediately  melted,  and 
drops  of  molten  glass  are  allowed  to  fall  into  a  cylinder  of 
water. 

Perhaps  the  most  remarkable  phenomenon  that  can  be 
produced  with  the  oxyhydrogen  flame  is  the  so-called  cal- 
cium light.  A  piece  of  quicklime  held  in  the  flame  is 
immediately  raised  to  a  brilliant  incandescence  of  almost 
blinding  intensity.  Other  highly  refractory  substances, 
such  as  magnesium  oxide,  may  also  be  raised  to  incandes- 
cence when  held  in  the  flame. 


66  CHEMICAL   LECTURE   EXPERIMENTS 

In  all  experiments  with  the  oxyhydrogen  flame  it  is 
advisable  to  protect  the  hands  with  gloves  and  the  eyes 
with  colored  glasses. 

Oxyhydrogen  blowpipe  or  burner ;  gas  blast-lamp ;  cupel  ;  0  and 
H  supply  ;  bundle  of  iron  wires  ;  Cu  and  Pt  wires  ;  pieces  of  Ag,  Pb, 
Cd  ;  quicklime. 

29.  Explosion  of  hydrogen  and  air.  —  (a)  A  round* 
bottomed  thick-walled  "ginger-ale''  bottle  is  marked  in 
sevenths.  Two-sevenths  of  its  volume  are  filled  with  hydro- 
gen over  the  pneumatic  trough,  and  by  lifting  the  mouth 
of  the  bottle  and  allowing  the  water  to  run  out,  the  re- 
maining five-sevenths  are  filled  with  air.  On  closing  the 
mouth  of  the  bottle  with  the  thumb,  and  inverting  it  once 
or  twice,  the  gases  will  rapidly  mix,  and  when  a  taper  is 
applied  to  the  mouth,  a  sharp  explosion  will  result.  A  good 
stout  bottle  should  stand  the  force  of  the  explosion,  though, 
unless  previously  tested,  it  is  well  to  cover  the  bottle  with 
a  towel. 

Round-bottomed  ginger-ale  bottle  ;  H  generator. 

(b)  A  bulb-tube  is  filled  with  hydrogen  by  allowing  the 
gas  to  flow  through  the  upper  end  of  the  tube,  when  held 
vertically,  and  thereby  to  push  out  the  air  at  the  bottom. 
When  full,  the  rubber  tube  through  which  the  hydrogen 
flows  is  removed  from  the  upper  end  of  the  bulb-tube  and  a 
flame  applied.  The  hydrogen,  being  lighter  than  air,  rises 
rapidly  in  the  tube  and  burns  at  the  top.  In  a  few  minutes 
the  air  entering  the  bottom  of  the  tube  will  have  mixed 
with  the  hydrogen  in  explosive  proportions,  and  the  flame 
will  strike  downwards  from  the  mouth  of  the  tube,  produc- 
ing a  sharp,  though  harmless,  explosion.  The  internal 
diameter  of  the  arms  of  the  bulb-tube  should  not  be  greater 
than  5  or  6  mm.     In  case  the  tubing  is  larger  than  this,  it  is 


OXYHYDROGEN    GAS    AND   WATER 


67 


advisable  to  choke  the  upward  flow  of  the  gas  by  inserting 
in  the  upper  arm-  of  the  bulb  a  small  piece  of  glass  tubing 
thrust  through  a  small  cork,  or  through  a  short  piece  of 
rubber  tubing. 

Bulb-tube  ;  H  generator. 

(c)  The  preceding  experiment  may  be  performed  with  an 
equal  degree  of  safety  on  a  much  larger  scale  by  using  a 
tubulated  liter  bell-jar,  the  tubulature  of  which 
is  fitted  with  a  cork  containing  a  short  piece 
of  tubing  6  mm.  in  diameter  (Fig.  32).  The 
bell-jar  is  filled  with  hydrogen,  either  by 
sending  a  slow  stream  of  the  gas  in  at  the 
top  through  the  glass  tube,  thus  forcing  out 
the  air  at  the  bottom,  or  at  the  pneumatic 
trough,  in  which  latter  case  it  will  be  neces- 
sary to  plug  the  glass  tube  temporarily  by  a 
short  piece  of  rubber  tubing  and  a  bit  of  glass 
rod.  The  hydrogen  is  lighted  at  the  top  of 
the  glass  tube,  and  burns  regularly,  as  it  is 
forced  out  by  the  air  rising  from  the  bottom. 
In  a  few  minutes  the  explosive  mixture  with  air  is  formed, 
and  the  flame  strikes  downwards  through  the  glass  tube, 
causing  an  explosion  in  the  bell-jar. 

Tubulated  liter  bell-jar  ;  H  generator. 

30.  Explosion  of  a  hydrogen  generator.  —  (a)  To  illus- 
trate the  explosive  nature  of  a  mixture  of  hydrogen  and 
air  and  the  consequent  danger  of  applying  a  lighted  taper 
to  a  hydrogen  generator  before  all  the  air  has  been  driven 
out,  a  stout  round-bottomed  ginger-ale  bottle  is  used  for  the 
generator,  as,  owing  to  its  strength,  it  will  suffer  no  damage 
by  an  internal  explosion  (Fig.  33).  Ten  grams  of  granulated 
zinc  are  placed  in  the  bottle,  which  is  clamped  in  an  up- 


FiG.  32 


CHEMICAL   LECTURE   EXPERIMENTS 


right  position,  and  8  cc.  of  dilute  sulphuric  acid,  made  by 
adding  1  cc.  of  concentrated  sulphuric  acid  to  7  cc.  of 
water  in  a  test-tube  are  poured,  while  still  warm 
from  the  act  of  dilution,  into  the  bottle.  A 
well-fitting  one-holed  cork,  carrying  a  10  cm. 
V  length  of  oiled  paper  tube,  such  as  is  used  in 
drinking  beverages,  is  loosely  placed  in  the  mouth 
of  the  bottle  and  the  tip  of  the  paper  immedi- 
ately ignited.  The  burning  paper  soon  ignites 
the  explosive  mixture  of  hydrogen  and  air  which 
strikes  back  into  the  bottle,  producing  a  sharp 
explosion  and  blowing  out  the  cork.  While  care 
should  be  taken  not  to  direct  the  bottle  toward 
any  one,  the  nature  of  the  cork  and  the  paper 
Fig  33       ^^^®  ^^  such  as  to  cause  no  damage. 

Ginger-ale   bottle ;    10    cm.    paper    tube    (artificial    bar    straw)  ; 
granulated  Zn. 

(b)  A  more  striking  illustration  of  the  danger  of  explosion 
of  a  hydrogen  generator  by  premature  lighting  is  shown  by 
means  of  the  following  apparatus.  A 
250  cc.  Erlenmeyer  flask,  preferably  of 
very  thin  glass,  is  fitted  with  a  two- 
holed  stopper  carrying  a  thistle-tube 
and  a  glass  elbow.  A  few  scraps  of 
zinc  are  placed  in  the  bottom  of  the 
flask  and  5  cc.  of  concentrated  hydro- 
chloric acid  poured  into  the  thistle- 
tube.  A  candle  fastened  on  a  wire  is 
placed  with  its  flame  at  the  end  of  the 
glass  elbow  which  serves  as  a  delivery-  fig.  34 

tube  for  the  gas.     To  retard  the  action 
of  the  hydrochloric  acid  on  the  zinc  in  order  to  afford  time 
for  lighting  the  candle  and  properly  covering  the  apparatus. 


OXYHYDROGEN   GAS    AND    WATER  69 

the  lower  end  of  the  thistle-tube  is  drawn  out  into  a  fine  point, 
allowing  the  acid  to  fall  drop  by  drop  (Fig.  34).  Soon  the 
mixture  of  hydrogen  and  air  assumes  the  right  proportion 
for  the  mixture  to  strike  back  through  the  glass  elbow  into 
the  flask,  producing  an  explosion  which  will  destroy  the 
whole  apparatus.  In  order  to  protect  the  audience,  it  is 
necessary  either  to  cover  the  entire  apparatus  with  a  small 
wooden  box,  or  better,  to  surround  it  with  heavy  glass 
screens.  Instead  of  a  thistle-tube,  a  piece  of  glass  tubing 
may  be  used,  of  which  the  lower  end  is  drawn  out  into  a  fine 
point,  and  the  upper  end,  extending  but  a  short  distance 
above  the  cork,  is  joined  with  a  small  glass  funnel  by  means 
of  a  rubber  connector.  In  this  arrangement  the  glass 
funnel  is  seldom  broken. 

250  cc.  Erlenmeyer  flask ;  thistle-tube  ;  glass  elbow ;  two-holed 
rubber  stopper  ;  wooden  box  or  glass  shields  ;  candle  ;  scrap  Zn. 

31.  Explosion  of  hydrogen  and  oxygen.  —  (a)  While  the 
explosion  of  hydrogen  and  diluted  oxygen,  i.e.,  atmospheric 
air,  is  sharp,  that  produced  by  the  ignition  of  a  gaseous 
mixture  consisting  of  two  parts  hydrogen  and  one  part 
oxygen  is  very  violent,  necessitating  considerable  care  in  its 
demonstration. 

The  round-bottomed  bottle  used  in  Ex.  29  is  two-thirds 
filled  with  hydrogen  over  the  pneumatic  trough,  and  the 
remaining  one-third  with  oxygen.  On  shaking  the  bottle 
for  a  moment,  the  gases  become  sufficiently  mixed  to  produce 
a  violent  explosion  when  a  taper  is  applied.  It  is  advisable 
to  wrap  the  bottle  in  two  or  three  layers  of  towel.  As  the 
proportions  in  which  the  gases  are  mixed  should  be  approx- 
imately correct,  the  bottle  is  roughly  graduated  by  pasting  a 
strip  of  paper  on  the  outside  indicating  two-thirds  of  its 
volume. 

Round-bottomed  ginger-ale. bottle  ;  H  and  0. 


70  CHEMICAL    LECTURE   EXPERIMENTS 

(6)  The  explosion  of  a  half  liter  of  oxyhydrogen  gas  may 
be  safely  accomplished  by  placing  a  flask  filled  with  the  gas 
under  a  box,  and  exploding  the  mix- 
ture with  an  electric  current  (Fig.  35). 
A  500  cc.  flask  is  two-thirds  filled 
with    hydrogen    and    the    remaining 
third    with    oxygen.       A    two-holed 
Fig.  'So  rubber    stopper    carrying   stout   rods 

of  brass,  which  extend  to  the  centre 
of  the  flask,  is  then  inserted  in  the  neck.  The  inner  ends 
of  the  brass  rods  should  be  electrically  connected  with  a 
piece  of  very  fine  platinum  wire  (Ex.  14).  The  flask  is  then 
placed  on  a  piece  of  asbestos  paper  on  the  table  and  covered 
with  a  small  wooden  box,  which  is  in  turn  covered  with  a 
larger  box.  The  larger  box  should  be  raised  one  inch  from 
the  table  by  small  blocks  of  wood  at  each  corner.  Two  lead 
wires  are  brought  from  the  brass  rods  to  the  bichromate 
battery,  which  may  be  placed  at  some  distance  from  the 
box.  On  making  the  connection,  the  platinum  wire  is  heated 
to  redness  and  the  gaseous  mixture  is  exploded.  While  it 
is  not  uncommon  to  have  the  small  box  destroyed  by  the 
force  of  the  explosion,  the  large  box  will  not  be  damaged. 
The  glass  flask  will  be  reduced  to  a  fine  powder. 

500  cc.  flask  ;  2-holed  rubber  stopper  ;  two  brass  rods  ;  fine  Pt  wire  ; 
small  and  large  wooden  boxes  ;  asbestos  paper  ;  bichromate  battery  ; 
connecting  wires  ;  H  supply  ;  0  supply. 

32.  Explosion  of  oxyhydrogen  soap-bubbles.  —  (a)  Soap- 
bubbles  are  blown  with  the  oxyhydrogen  mixture  in  a 
thistle-tube  as  described  in  Ex.  13.  On  being  liberated 
they  rise  slowly  through  the  air,  and  are  easily  ignited 
by  touching  with  a  small  wax  candle  on  the  end  of  a  stick. 
It  is  of  the  utmost  importance  that  no  particles  of  burn- 
ing paper  or  other  material  should   be  allowed  to   come 


OXYHYDROGEN   GAS   AND    WATER  71 

in  contact  with  the  thistle-tube  by  which  the  bubbles  are 
blown,  as  a  dangerous  explosion  would  result  by  the  striking 
back  of  the  explosive  gaseous  mixture  into  the  holder.  It  is 
advisable  to  use  a  non-sparking  material  for  a  taper,  such  as 
a  small  wax  candle  firmly  fastened  on  a  long  stick.  The 
glass  funnel  used  in  igniting  bubbles  filled  with  hydrogen 
(Fig.  21,  p.  52)  may  be  used  here  to  advantage. 

Oxyhydrogen  gas  ;  thistle-tube  ;  soap  solution  ;  candle  on  stick. 

(b)  A  small  quantity  of  soap  solution  is  placed  in  the 
bottom  of  a  large  iron  mortar  or  dish,  and  a  handful  of  soap- 
bubbles  blown  by  directing  a  stream  of  mixed  hydrogen  and 
oxygen  through  it.  After  removing  the  tube  conducting  the 
mixed  gases,  the  soap-bubbles  are  exploded  by  means  of 
a  candle  on  the  end  of  a  long  stick.  The  concussion  is  so 
great  that  only  a  small  volume  of  the  mixed  gases  should 
be  exploded  at  one  time. 

33.  Electrolysis  of  water  and  the  preparation  of  oxy- 
hydrogen gas.  —  A  simple  apparatus  for  the  electrolysis  of 
water  is  shown  in  Fig.  5,  p.  14,  and  consists  of  a  small  wide- 
mouthed  bottle  with  a  three-holed  rubber  stopper.  Glass 
tubes  carrying  platinum  electrodes  are  fitted  into  two  of  the 
holes,  and  a  delivery-tube  thrust  into  the  third  hole  leads  to  a 
pneumatic  trough.  The  end  of  the  delivery-tube  must  not 
be  thrust  clear  through  the  cork.  The  bottle  is  filled  to 
overflowing  with  10  per  cent  sulphuric  acid,  and  the  cork 
pushed  down  into  the  flask  in  such  a  manner  that  the  dilute 
acid  will  fill  the  delivery -tube,  expelling  all  air.  Before  turn- 
ing on  the  electric  current,  care  should  be  taken  that  the 
platinum  electrodes  are  as  far  apart  as  possible  in  the  vessel. 
On  allowing  the  current  from  three  or  four  bichromate  cells 
to  pass  through  the  solution,  a  rapid  evolution  of  hydrogen 
and  oxygen  takes  place.     The  mixed  gases  may  be  collected 


72        CHEMICAL  LECTURE  EXPERIMENTS 

in  a  eudiometer  (Fig.  11,  p.  26)  at  the  pneumatic  trough. 
The  eudiometer  is  transferred  to  another  dish  by  placing  the 
thumb  on  the  bottom  of  the  tube,  and  potassium  pyrogallate 
solution  is  allowed  to  flow  through  the  mixed  gases  and 
absorb  the  oxygen.  When  the  absorption  is  complete,  it  will 
be  found  that  the  residual  gas,  which  will  burn  quietly,  is 
two-thirds  of  the  original  volume. 

If  the  delivery-tube  dips  sufficiently  beneath  the  surface 
of  the  water  in  the  pneumatic  trough  to  disengage  the 
bubbles  (to  prevent  the  explosion  from  striking  back  into 
the  bottle)  from  the  delivery -tube  before  reaching  the  surface 
of  the  water,  they  may  be  exploded  by  holding  a  match  or 
gas-jet  at  the  surface  of  the  water. 

Electrolytic  apparatus  (Fig.  5,  p.  14)  ;  eudiometer  (Fig.  11,  p.  26)  ; 
four  bichromate  cells ;  H2SO4  (10  per  cent)  ;  potassium  pyrogallate 
solution  (Ex.  21,  p.  26). 

34.  Electrolysis  of  water.  —  (a)  The  decomposition  of 
water  by  the  electric  current  with  the  separation  of  the  two 
gases,  hydrogen  and  oxygen,  in  their  relative  volumes  two  to 
one,  is  shown  by  the  use  of  the  apparatus  (Fig.  46,  p.  95) 
which,  of  the  many  forms  of  electrolytic  apparatus  described 
by  Hoffmann,  is  the  one  best  adapted  for  many  experiments. 
The  electrodes  here  used  are  made  by  passing  small  glass 
tubes  through  one-holed  rubber  stoppers  inserted  in  the  two 
lower  openings  of  the  apparatus.  Through  these  glass  tubes 
platinum  wires  are  passed  and  fused  to  prevent  any  escape 
of  the  liquid  through  the  glass  tube.  Small  pieces  of  plat- 
inum foil  are  fastened  to  the  ends  of  the  wire,  thus  giving 
greater  surface  to  the  electrodes.  The  glass  portion  of  the 
apparatus  is  mounted  on  a  specially  devised  iron  stand. 
After  use  the  apparatus  should  be  thoroughly  rinsed  with 
water,  the  rubber  stoppers  carrying  the  electrodes  removed, 
and  the  glass  stop-cocks   either  removed  and  tied  with  a 


OXYHYDROGEN    GAS   AND   WATER  73 

piece  of  twine  to  their  respective  tubes,  or  wedged  into  their 
openings  with  a  piece  of  paper.  When  properly  handled 
such  an  apparatus  should  last  for  years. 

For  the  electrolysis  of  water  the  stop-cocks  are  closed  and 
the  open  bulb  filled  with  10  per  cent  sulphuric  acid,  the  elec- 
trodes having  been  tightly  inserted.  On  opening  the  stop-cock 
the  solution  will  rise,  expelling  the  air,  and  in  case  it  is  de- 
sired to  ignite  the  hydrogen  after  electrolysis,  care  should  be 
taken  to  allow  no  water  to  enter  the  hole  drilled  through  the 
glass  stop-cock,  or  the  bit  of  tube  extending  beyond.  In 
case  water  should  reach  these  portions,  it  should  be  removed 
by  a  strip  of  filter-paper  rolled  into  a  fine  point,  as  other- 
wise on  opening  the  cock  drops  of  water  will  be  forcibly 
ejected,  and  may  easily  extinguish  a  match  or  taper  used  to 
test  the  gas.  As  at  best  there  is  not  a  large  quantity  of  gas 
to  be  experimented  with,  all  precautions  should  be  taken 
that  none  is  wasted.  Having  filled  both  arms  of  the  tube, 
the  current  from  four  or  more  cells  of  a  bichromate  battery 
may  be  sent  through  the  apparatus,  and  immediately  bub- 
bles will  rise  from  both  electrodes.  After  a  few  minutes  it 
will  be  observed  that  twice  as  much  gas  will  have  collected 
in  one  tube  as  in  the  other. 

On  holding  a  glowing  splinter  over  the  tube  containing 
the  smaller  volume  of  gas,  proof  may  be  had  of  the  presence 
of  oxygen.  The  gas  issuing  from  the  other  jet  when  opened 
may  be  ignited  and  shown  to  be  hydrogen.  If  the  tip  of  the 
glass  tube  is  moistened  with  strong  sodium  chloride  solution, 
the  hydrogen  flame  will  be  sufficiently  colored  to  be  seen  at 
a  distance.  211,0  =  2  K,  +  0,. 

Hoffmann  electrolytic  apparatus  (Fig.  46,  p.  95) ;  four  cells  bichro- 
mate battery  ;  10  per  cent  H2SO4. 

(6)  The  decomposition  of  acidulated  water  by  the  electric 
current  may  be  much  more  simply  effected  by  using  the 


74 


CHEMICAL  LECTURE  EXPERIMENTS 


apparatus  shown  in  Fig.  36.  The  electrodes  of  this  appa- 
ratus are  prepared  by  sealing  a  short  piece  of  platinum 
wire  fastened  to  a  piece  of  platinum  foil  into  a  drawn-out 

tube  bent  in  the  form  of  a 

hook.    The  tube  is  then  filled 
with  mercury,  and  the  con- 
nections are  made  by  thrust- 
ing the   lead  wires   from   a 
battery  into  the  mercury  in 
the  tube.     Two  glass  cylin- 
ders of   equal  diameter  are 
filled    with    the    acidulated 
water  and  inverted  over  the 
electrodes. 
The  electrodes  may  be  still  further  simplified  by  fasten- 
ing pieces  of  platinum  foil  to  rubber-covered  copper  wire. 
It  is  necessary  in  this  case,  however,  to  cover  with  paraffin 
all  parts  of  exposed  copper. 


Fig.  36 


HYDROGEN    PEROXIDE 

FORMATION   AND    PREPARATION 

35.  By  cooling  a  jet  of  burning  hydrogen.  —  When  a 
flame  of  burning  hydrogen  is  suddenly  cooled,  small  quanti- 
ties of  hydrogen  peroxide  are  formed. 

Hydrogen  obtained  from  the  action  of  zinc  on  dilute  sul- 
phuric acid  is  allowed  to  burn  from  a  glass  jet,  3  or  4  mm. 
in  diameter,  directed  downwards  upon 
water  in  a  porcelain  evaporating  dish, 
which  has  a  few  pieces  of  ice  floating 
in  it.  Two  or  three  drops  of  dilute 
sulphuric  acid  should  be  added  to 
the  water  in  the  dish.  The  jet  flame  is  so  played  on  the 
surface  of  the  water  as  to  cool  about  one-half  of  it,  and  is 


Fig.  37 


HYDROGEN   PEROXIDE  75 

allowed  to  burn  in  this  way  for  two  or  three  minutes.     The 
jet  should  be  clamped  in  the  proper  position. 

The  liquid  is  tested  by  adding  some  potassium  iodide- 
starch  solution,  to  which  a  drop  of  ferrous  sulphate  solution 
has  been  added.  A  blue  color  indicates  the  presence  of 
hydrogen  peroxide. 

H  from  Zn  and  H2SO4  ;  ice  ;  KI  starch  solution  ;  FeSOi  solution. 

36.  By  the  action  of  sodium  peroxide  on  water.  —  When 
small  quantities  of  water  are  added  to  sodium  peroxide,  oxy- 
gen is  liberated,  sodium  hydroxide  being  formed  (Ex.  5, 
p.  11).  If  small  quantities  of  the  peroxide  are  added  to  a 
large  quantity  of  water,  the  oxygen  is  not  liberated  but  is 
retained  as  hydrogen  peroxide. 

One  hundred  cubic  centimeters  of  cold  water,  to  which 
5  cc.  of  sulphuric  acid  have  been  added,  are  placed  in  a 
beaker  into  which  2  or  3  g.  of  sodium  peroxide  are  allowed 
to  fall  slowly.  The  liquid  should  be  constantly  stirred. 
After  the  addition  of  the  sodium  peroxide  the  liquid,  which 
should  still  be  strongly  acid,  will  contain  considerable  quan- 
tities of  hydrogen  peroxide. 

NagOa  +  2  H2O  =  2  NaOH  +  H2O2. 

37.  From  barium  peroxide  and  sulphuric  acid.  —  Concen- 
trated sulphuric  acid  acts  on  barium  peroxide  to  produce 
oxygen  which  under  75°  C.  is  rich  in  ozone  (Ex.  30,  p.  31). 

When,  however,  dilute  sulphuric  acid  and  barium  perox- 
ide are  allowed  to  interact  under  conditions  which  maintain 
the  mixture  at  a  low  temperature,  considerable  quantities 
of  hydrogen  peroxide  are  formed. 

A  handful  of  crushed  ice  is  placed  in  a  beaker  and  a  few 
grams  of  barium  peroxide,  stirred  in  with  it.  Enough  dilute 
sulphuric  acid  is  added  to  cover  the  ice,  and  the  liquid  is  fil- 


76  CHEMICAL   LECTURE   EXPERIMENTS 

tered  off  from  the  insoluble  barium  sulphate  formed.  The 
filtrate  contains  hydrogen  peroxide,  which  may  be  used  for 
any  of  the  following  experiments. 

With  care  the  method  with  slight  alterations  will  give  a 
chemically  pure  solution  of  hydrogen  peroxide.  Such  a 
solution  is,  however,  readily  obtained  in  the  market. 

BaOa  +  H2SO4  =  H2O2  +  BaSO^. 
Crushed  ice ;  Ba02. 

PROPERTIES 

38.  Action  on  potassium  dichromate.  —  In  a  dilute  acidu- 
lated solution,  potassium  dichromate  reacts  with  hydrogen 
peroxide,  giving  an  intense  blue  color  due  to  the  formation 
of  perchromic  acid.  This  reaction  serves  to  identify  small 
quantities  of  hydrogen  peroxide. 

A  very  dilute  solution  of  potassium  dichromate,  contain- 
ing a  few  drops  of  sulphuric  acid,  is  placed  in  a  stoppered 
glass  cylinder  and  1  cc.  of  hydrogen  peroxide  is  added. 
The  liquid  is  colored  intensely  blue.  If  one-half  of  the 
solution  is  poured  into  a  small  cylinder  and  allowed  to  stand 
for  a  few  moments,  the  color  rapidly  disappears. 

A  1.5  cm.  layer  of  ether  is  added  to  the  remaining  solu- 
tion in  the  stoppered  cylinder  and  the  cylinder  shaken.  On 
standing,  the  ether  will  separate  and  will  acquire  the  deep 
blue  color,  which  will  have  disappeared  from  the  liquid 
beneath. 

100  cc.  stoppered  cylinder  ;  H2O2 ;  K2Cr207  solution  ;  ether. 

39.  Action  on  lead  sulphide.  —  The  oxidizing  action  of 
hydrogen  peroxide  in  converting  a  sulphide  to  a  sulphate  is 
shown  by  the  conversion  of  black  lead  sulphide  to  white  lead 
sulphate.  To  a  small  quantity  of  freshly  precipitated  lead 
sulphide  suspended  in  water  a  few  cubic  centimeters  of 


( 


HYDROGEN   PEROXIDE  77 

hydrogen  peroxide  are  added.  Immediately  the  black  sul- 
phide is  oxidized  to  the  white  sulphate.  By  dipping  filter- 
paper  in  a  solution  of  lead  acetate  and  exposing  it  to  the 
fumes  of  hydrogen  sulphide,  black  lead  sulphide  is  formed 
on  the  paper.  On  immersing  the  blackened  paper  in  hydro- 
gen peroxide  solution,  the  paper  becomes  colorless. 

PbS  +  4  HA  =  PbS04  +  4  H2O. 
Freshly  precipitated  PbS  suspended  in  water  ;  H202. 

40.  Oxidizing   action   on  zinc   and  sulphuric   acid.  —  A 

small  piece  of  zinc  placed  in  a  test-tube  is  covered  with 
about  10  cc.  of  water,  and  then  1  drop  of  concentrated  sul- 
phuric acid  added.  Almost  immediately  the  evolution  of 
hydrogen  takes  place,  and  the  liquid  is  seen  to  be  opaque  as 
a  result  of  the  bubbles.  On  adding  an  equal  volume  of 
acidulated  hydrogen  peroxide,  the  gas  evolution  immediately 
ceases  and  the  solution  becomes  clear. 

That  this  cessation  of  the  evolution  of  the  gas  may  not 
be  the  result  of  dilution,  the  hydrogen  peroxide  should  con- 
tain enough  sulphuric  acid  to  maintain  the  solution  at  or 
above  the  original  percentage  of  acid. 

H20o  +  H2  =  2H20. 

Acidulated  H2O2  solution  ;  granulated  Zn. 

41.  Electrolysis  of  hydrogen  peroxide.  —  The  rapid  oxi- 
dation of  nascent  hydrogen  by  a  solution  of  hydrogen  per- 
oxide is  well  shown  when  the  electric  current  is  used  to 
produce  an  evolution  of  hydrogen  in  an  acidulated  solution 
of  hydrogen  peroxide. 

A  small  cylinder  is  filled  with  a  10  per  cent  solution  of  sul- 
phuric acid.  A  similar  cylinder  is  filled  with  hydrogen  per- 
oxide which  contains  a  few  drops  of  concentrated  sulphuric 
acid.     The  solutions  in  the  cylinders  are  electrically  con- 


78 


CHEMICAL   LECTURE   EXPERIMENTS 


Fig.  38 


nected  by  means  of  a  loop  of  platinum  wire  dipping  into  the 
liquid  in  each  cylinder  (Fig.  38).     Electrodes  consisting  of 
small  pieces  of  sheet  platinum  are  dipped 
X^  £\     into  each  cylinder  and  the  circuit  of  a 

^         _  ^     bichromate   battery   thereby  closed.      If 

the  positive  electrode  is  immersed  in  the 
dilute  sulphuric  acid,  a  rapid  evolution  of 
hydrogen  will  take  place  and  the  liquid 
will  become  turbid  from  the  ascending 
bubbles.  The  negative  electrode,  i.e.,  the 
one  immersed  in  the  peroxide  of  hydro- 
gen solution,  will  also  give  rise  to  a  gas  evolution.  If  now 
the  current  be  reversed  or  the  electrodes  transposed,  it  will 
be  found  that  the  electrode  immersed  in  the  hydrogen  per- 
oxide solution  gives  no  gas  evolution  if  the  battery  is  not 
too  strong,  while  that  immersed  in  the  dilute  sulphuric  acid 
acts  as  before.  In  this  case  the  nascent  hydrogen  liberated 
by  the  electrolytic  action  is  oxidized  by  the  hydrogen  per- 
oxide as  fast  as  formed. 

When  acidulated  hydrogen  peroxide  is  electrolyzed  with 
platinum  electrodes  in  the  Hoffmann  apparatus  (Fig.  46, 
p.  95),  a  gas  collects  only  in  one  arm  of  the  tube,  the  hydro- 
gen being  oxidized  as  fast  as  formed  by  the  hydrogen 
peroxide. 

Bichromate  battery,  two  or  three  cells  ;  Pt  wires ;  Pt  electrodes ; 
Hoffmann  electrolytic  apparatus  (Fig.  46,  p.  95)  ;  H2O2 ;  10  per 
cent  H2SO4. 


42.  Bleaching  action.  —  Hydrogen  peroxide,  when  not 
too  acid,  bleaches  organic  matter  readily.  This  bleaching 
action  is  best  shown  by  adding  to  a  solution  of  aniline  red 
a  few  cubic  centimeters  of  hydrogen  peroxide.  If  the 
reagent  is  not  too  acid,  the  color  will  be  discharged  on 
boiling. 


HYDROGEN   PEROXIDE  79 

If  acid  is  added  to  the  hydrogen  peroxide,  the  mixture  of 
aniline  red  and  the  reagent  can  be  boiled  with  no  appreci- 
able change  in  color,  as  the  acidulated  solution  of  the  per- 
oxide is  very  stable.  On  adding  a  few  drops  of  sodium 
hydroxide  to  the  hot  solution,  the  color  is  instantly  dis- 
charged 

If  the  hydrogen  peroxide  solution  is  made  alkaline  and 
then  added  to  the  aniline  red,  the  color  is  discharged  instantly 
even  in  the  cold. 

Aniline  red :  H2O2. 


CHLOEINE 


CHLORINE 

PREPARATION 

^  1.  From   manganese   dioxide   and   hydrochloric   acid. — 

Concentrated  hydrochloric  acid  when  mixed  with  manga- 
nese dioxide  and  gently  heated  yields  chlorine. 

A  2  1.  flask  is  one-fourth  filled  with  coarsely  pulverized 
(not  powdered)  manganese  dioxide.  Sufficient  concentrated 
hydrochloric  acid  is  added  to  cover  the  solid  and  the  mix- 
ture is  heated  with  a  low  flame.  A  two-holed  rubber  stopper 
carrying  a  bulb  safety-tube  and  a  glass  elbow  is  inserted  in 
the  neck  of  the  flask.  The  gas  is  first  conducted  through  a 
gas  washing-bottle  containing  a  small  quantity  of  water,  then 
through  a  three-way  cock  into  a  second  gas  washing-bottle 
containing  sulphuric  acid.  The  third  arm  of  the  three-way 
cock  (Fig.  39)  is  connected  with  a  flue.  The  bend  of  the 
safety-tube  is  filled  with  concentrated  sulphuric  acid  or 
mercury.  By  means  of  the  three-way  cock  the  gas  may  be 
conducted  into  the  flue  until  desired  and  then  by  turning  the 
cock  may  be  passed  through  the  sulphuric  acid  into  any 
apparatus. 

Though  no  difficulty  should  be  experienced  in  properly 
turning  the  three-way  cock  it  is  easy  to  note  by  the  bubbling 
in  the  sulphuric  acid  bottle  whether  or  no  the  gas  is  properly 

80 


CHLORINE 


81 


directed.  In  case  the  cock  should  be  so  turned  as  to  cut 
the  exit  of  the  gas  off  entirely,  the  rise  of  the  sulphuric  acid 
or  mercury  in  the  safety-funnel  as  well  as  the  absence  of 
bubbles  in  the  gas  washing-bottle  containing  water  will  be 
immediately  noticed.  The  stopper  used  in  the  generating 
flask  should  be  of  rubber,  and  both  the  safety-tube  and 

the  glass  elbow  should  fit  snugly 
into  the  respective  holes.  Chlo- 
rine will  in  course  of  time  attack 
rubber  and  render  it  hard  and 
unsuited  for  use.  By  coating 
the  under  side  of  the  stopper 
with  collodion  just  before  insert- 
ing it  in  the  flask,  the  action  of 


^TT" 


=□= 


^ 


P^iG.  39 


the  chlorine  may  be  very  much  lessened.  The  water  in  the 
gas  washing-bottle  removes  traces  of  hydrochloric  acid  car- 
ried over,  and  the  gas  issuing  from  the  sulphuric  acid  bottle 
is,  accordingly,  quite  pure.  In  case  a  flue  is  not  at  hand, 
the  waste  gas  issuing  from  the  stem  of  the  three-way  cock 
should  be  conducted  through  a  glass  tube  into  potassium  or 
sodium  hydroxide  solution. 

;-  MnOs  -f  4  HCl  =  MnCla  -f  2  H2O  4-C12. 

Apparatus  (Fig.  39)  ;  2  1.  flask ;  two  gas  washing-bottles ;  three- 
way  cock ;  safety-tube  ;  2-holed  rubber  stopper ;  coarsely  pulverized 
MnOa. 


I 


82  CHEMICAL   LECTURE   EXPERIIVIENTS 

^  2.  By  the  action  of  sulphuric  acid  on  a  mixture  of  sodium 
chloride  and  manganese  dioxide.  —  Instead  of  acting  directly 
on  manganese  dioxide  with  hydrochloric  acid,  the  acid  may 
be  prepared  in  the  presence  of  manganese  dioxide,  where  it 
is  immediately  oxidized  with  the  liberation  of  chlorine. 
The  apparatus  used  is  shown  in  Fig.  39. 

One  hundred  grams  of  finely  pulverized  manganese  dioxide 
are  mixed  with  an  equal  weight  of  sodium  chloride,  and  the 
mixture  is  placed  in  the  generating  flask.  One  hundred  and 
ten  cubic  centimeters  of  concentrated  sulphuric  acid  are 
poured  slowly  into  100  cc.  of  water  in  a  beaker  and  the 
mixture  cooled.  The  dilute  acid  is  then  poured  into  the 
generating  flask  upon  the  manganese  dioxide  and  sodium 
chloride.  The  flask  is  well  shaken  for  a  moment  and  the 
cork  immediately  inserted.  A  rapid  stream  of  chlorine, 
which  may  be  maintained  by  the  application  of  a  gentle 
heat,  is  obtained. 

4  NaCl  -h  MnOa  +  3  H2SO4  =  2  NaHS04  +  NaaSO^  + 
MnCl2  +  2  H2O  +  CI2. 

Apparatus  (Fig.  39)  ;  finely  pulverized  Mn02  ;  NaCl ;  acid  mixture 
(110  cc.  H2SO4  +  100  cc.  H2O). 

3.  From  hydrochloric  acid  and  potassium  dichromate.  — 

Potassium  dichromate  oxidizes  hydrochloric  acid,  yielding 
chlorine  free  from  carbon  dioxide.  The  apparatus  (Fig.  39) 
is  used,  and  500  cc.  of  concentrated  hydrochloric  acid  are 
poured  upon  100  g.  of  coarsely  pulverized  potassium  dichro- 
mate in  the  generating  flask.  By  gently  heating  over  a  wire 
gauze  a  rapid  stream  of  pure  chlorine  is  obtained. 

K2Cr207  +  14  HCl  =  2  KCl  +  2  CrCls  +  7  H2O  +  3  CI2. 

Apparatus  (Fig.  39)  ;  KsCisOt. 

4.  By  the  action  of  a  mixture  of  gaseous  hydrochloric  acid 
and  air  on  heated  copper  salts  (Deacon's  process). — An  in- 


CHLORINE  83 

teres  ting  process  for  the  technical  manufacture  of  chlorine 
is  the  so-called  "  Deacon's  process/'  in  which  a  mixture  of  air 
and  hydrochloric  acid  is  conducted  over  a  heated  copper  salt. 

Small  fragments  of  pumice-stone,  sufficient  to  fill  a  bulb- 
tube,  are  heated  in  an  evaporating  dish  with  a  strong  solu- 
tion of  copper  sulphate  or  copper  chloride  until  all  water  of 
crystallization  is  driven  from  the  salt.  The  bulb  is  then 
filled  with  the  prepared  pumice-stone.  A  mixture  of  air  and 
hydrochloric  acid  gas  is  obtained  by  allowing  the  gases  to 
enter  a  three-necked  Wolff  bottle  (Fig.  69,  p.  159)  and  bubble 
through  concentrated  sulphuric  aci^.  The  mixed  gases  issue 
through  the  third  neck  of  the  Wolff  bottle,  through  a  glass 
elbow  which  is  connected  with  one  end  of  the  bulb-tube.  The 
other  end  of  the  tube  is  fitted  with  a  rubber  stopper  and  an 
elbow  dipping  into  a  beaker  containing  a  solution  of  potas- 
sium iodide  and  starch.  The  gaseous  mixture  is  passed 
through  the  system  and  ho  color  is  obtained  in  the  beaker. 
On  heating  the  bulb  with  a  Bunsen  lamp  the  air  and  the 
hydrochloric  acid  gas  react  in  the  presence  of  the  copper 
salt  to  form  free  chlorine,  and  a  blue  color  immediately 
appears  in  the  beaker.  It  is  necessary  that  the  hydrochloric 
acid  gas  used  in  this  experiment  should  be  perfectly  free 
from  chlorine. 

Instead  of  preparing  gaseous  hydrochloric  acid  the  experi- 
ment can  be  more  simply  carried  out  by  conducting  a  gentle 
current  of  air  through  a  gas  washing-bottle  containing  con- 
centrated, chemically  pure  hydrochloric  acid.  In  passing 
through  the  bottle  sufficient  hydrochloric  acid  gas  will  be 
taken  up  by  the  air  current  to  react  when  passed  through 
the  heated   bulb  and  will  give  a  blue    coloration   in   the 

beaker. 

2  HCl  -f-  O2  =  H2O  -f  CI2  [?]. 

3-necked  Wolff  bottle  ;  bulb-tube  containing  pumice-stone  and 
CUSO4  ;  HCl  gas  supply  ;  air-blast ;  Kl-starch  solution. 


84  CHEMICAL   LECTURE   EXPERIMENTS 

PROPERTIES 

5.  Chlorine  water.  —  (a)  Chlorine  is  readily  absorbed  by 
water,  imparting  to  it  a  greenish  color  and  many  of  the 

properties    of    the 
gas. 

A  retort  is  com- 
pletely filled  with 
YiG,  40  ^"^^^"^^^^^T^^  water  and  inverted 
as  in  Fig.  40.  Chlo- 
rine is  conducted  through  a  long  delivery-tube  in  the  neck 
of  the  retort,  and  the  body  is  about  half  filled  with  the  gas. 
The  absorption  is  quite  rapid,  and  in  a  short  time  the  water 
has  a  decided  greenish  color. 
600  cc.  retort ;  01  supply. 

(6)  The  preparation  of  any  considerable  quantity  of  chlo- 
rine water  is  best  effected  by  conducting  the  gas  through  a 
series  of  Wolff  bottles  (Fig.  85,  p.  196)  half  filled  with 
cold  water.  The  tube  through  which  the  gas  enters  each 
Wolff  bottle  should  dip  only  a  little  below  the  surface  of 
the  water.  Provision  should  be  made  for  absorbing  any 
gas  escaping  from  the  system  in  sodium  hydroxide  or  for 
conducting  it  to  a  flue. 

Apparatus  (Fig.  85,  p  196)  ;  CI  supply. 

6.  The  crystalline  hydrate  of  chlorine.  —  One  molecule  of 
chlorine  combines  with  ten  molecules  of  water  to  form  a 
white  crystalline  hydrate  (Clg  + 10  HgO)  which  decom- 
poses a  little  above  zero. 

A  current  of  chlorine  is  conducted  into  25  cc.  of  water  in 
a  100  cc.  flask  containing  a  few  small  pieces  of  ice.  Soon 
the  hydrate  is  formed,  and  the  liquid  in  the  flask  solidifies 
to  a  crystalline  mass. 

01  supply  ;  ice. 


CHLORINE 


86 


7.  Combustion  of  hydrogen  in  chlorine. — A  jet  of  burning 
hydrogen   when   lowered   into   an   atmosphere  of   chlorine 
continues  to  burn  with  a  blue 
flame,    forming    hydrochloric      ^^ 


acid. 

Hydrogen  is  conducted 
through  the  recurved  jet,  Fig. 
41,  and  lowered  into  a  liter 
cylinder  of  chlorine.  White 
fumes  of  hydrochloric  acid 
gas  rise  from  the  mouth  of 
the  cylinder,  and  a  piece  of 
blue  litmus  paper  is  reddened 
when  held  in  the  gas. 

A  jet  of  chlorine  burns  when  thrust  up  into  an  inverted 
cylinder  of  hydrogen  (Fig.  42). 


u 


Fig.  41 


Fig.  42 


H, 


CL 


2HC1. 


Recurved  jet  Fig.  41 ;  H  supply  ;  liter  cylinder  of  CI ;  litmus  paper 
(blue). 

8.   Explosion  of  a  mixture  of  chlorine  and  hydrogen. — 

A  mixture  of  equal  volumes  of  chlorifie  and  hydrogen  when 
ignited  explodes  with  considerable  force. 

A  100  cc.  stout-walled  cylinder  is  filled  with  chlorine  and 
placed  mouth  to  mouth  with  a  cylinder  of  the  same  size 
filled  with  hydrogen.  The  gases  are  mixed  by  shaking,  and 
the  cylinders  are  then  separated  and  covered  with  glass 
plates.  On  removing  the  plates  and  applying  a  flame  the 
mixture  exj)lodes  with  a  loud  report.  The  greatest  care 
should  be  taken  to  keep  the  mixed  gases  away  from  all 
direct  sunlight,  as  under  the  influence  of  bright  light  the 
gases  combine  with  explosion. 


100  cc.  cylinder  of  CI ;  100  cc.  cylinder  of  H. 


86  CHEMICAL  LECTURE   EXPERIMENTS 

^  9.  Combustion  of  a  candle.  —  The  gaseous  hydrocarbons 
volatilized  by  a  burning  candle  will  burn  in  chlorine  with 
the  liberation  of  carbon  in  the  form  of  soot.  A  burning 
candle  when  lowered  into  chlorine,  which  should  be  free 
from  any  great  amount  of  carbon  dioxide,  burns  with  a 
lurid,  smoky  flame,  large  quantities  of  soot  being  deposited. 
The  flame  is  easily  extinguished  and  at  best  burns  only  a 
few  moments. 

A  burning  splinter  thrust  into  chlorine  is  immediately 
extinguished. 

Candle  on  wire  ;  jar  of  CI. 

10.  Action  on  turpentine. — When  slightly  warmed  tur- 
pentine is  introduced  into  chlorine,  the  reaction  is  so  great 
that  the  turpentine  is  ignited. 

Three  or  four  cubic  centimeters  of  turpentine  are  warmed 
in  a  test-tube  and  poured  on  a  piece  of  filter-paper  or  cheese- 
cloth fastened  on  a  wire.  The  cloth  is  then  quickly  lowered 
into  a  liter  cylinder  of  chlorine.  In  a  few  moments  the 
turpentine  will  become  ignited  and  dense  clouds  of  soot  will 
pour  out  of  the  cylinder.  Obviously  the  experiment  should 
be  conducted  only  in  a  good  draft. 

Liter  cylinder  of  CI ;  turpentine  ;  filter-paper  on  wire. 

'"  11.    Bleaching.  —  (a)  Chlorine,    combining,    as    it    does, 

with  the  hydrogen  of  water  and  liberating  nascent  oxygen, 
is  a  powerful  bleaching  agent. 

A  piece  of  cloth  dyed  with  turkey  red  is  dampened  and 
lowered  into  a  cylinder  of  chlorine.  In  a  few  moments  the 
color  will  have  entirely  disappeared. 

The  importance  of  having  water  in  the  operation  of 
bleaching  with  chlorine  may  be  shown  as  follows :  A  piece 
of  turkey-red  cloth  which  has  been  dried  for  half  an 
hour  in  an  air-bath  immediately  before  use  is  lowered  into 


CHLORINE  87 

a  cylinder  of  chlorine  whicli  has  been  especially  dried  by 
shaking  the  gas  with  25  cc.  of  concentrated  sulphuric  acid. 
Care  should  be  taken  in  drying  the  gas  to  have  the  cylinder 
closed  with  a  glass  plate  to  avoid  spattering  the  acid.  If 
the  wire  on  which  the  piece  of  cloth  is  suspended  is  fastened 
to  a  piece  of  cardboard  large  enough  to  cover  the  mouth  of 
the  cylinder,  the  cloth  may  be  left  for  some  time  in  the  gas 
with  no  appreciable  change  of  color.  If  the  cloth  is  then 
removed  and  held  in  steam  for  a  few  moments  and  again 
introduced  into  the  gas,  the  color  is  almost  immediately  dis- 
charged. 

Two  cylinders  of  CI  (one  dried  by  shaking  with  con.  H2SO4)  ;  pieces 
of  turkey-red  cloth  ;  boiling  water  in  a  beaker. 

(6)  Chlorine  bleaches  many  organic  dyes  used  in  prepar- 
ing writing-inks,  though  it  is  without  action  on  carbon  in 
the  graphite  of  the  lead  pencil  and  the  lamp-black  of  print- 
ing-ink. 

A  piece  of  white  paper,  upon  which  several  characters  in 
printing-ink  have  been  stamped,  is  marked  with  a  lead 
pencil,  several  kinds  and  colors  of  writing-ink,  and  with  a 
blue  pencil.  The  paper  is  then  moistened  by  dipping  into 
water  and  thrust  into  a  cylinder  of  chlorine.  The  printing- 
ink  and  lead-pencil  marks  will  be  unaffected  by  the  chlorine. 
The  blue  pencil  is  ordinarily  turned  green,  and  the  writing- 
inks  will  for  the  most  part  be  entirely  bleached. 

Large  cylinder  of  CI ;  piece  of  paper  ;  colored  inks  ;  blue  and  black 
lead  pencils. 

12.   Decomposition  of  chlorine  water  by  sunlight.  — In  the 

presence  of  sunlight  chlorine  combines  with  the  hydrogen 
of  water,  forming  hydrochloric  acid  and  liberating  oxygen. 

A  eudiometer  tube  or  plain  glass  tube  sealed  at  one  end 
is  completely  filled  with  strong  chlorine  water,  inverted  in 
a  crystallizing  dish  containing  the  same  liquid,  and  clamped 


88 


CHEMICAL   LECTURE   EXPERIMENTS 


i^'a  vertical  position.  If  the  apparatus  is  placed  in  direct 
sunlight,  the  action  will  soon  begin,  and  fine  bubbles  of  gas 
will  x3ollect  in  the  top  of  the  tube.  The  reaction  requires 
some  time  for  completion,  though  on  standing  twenty-four 
hours  a  sufficient  quantity  of  gas  will  have  collected  in  the 
top  of  the  tube  to  be  tested.  A  glowing  splinter  thrust  into 
the  gas  will  be  rekindled.  See  also  apparatus  (Fig.  4,  p.  13). 
2  H2O  +  2  CI2  =  4  HCl  +  O2 
Eudiometer  tube  ;  strong  CI  water. 

13.  Action  on  brass.  —  (a)  Thin  brass  or  so-called  Dutch 
metal  leaf  burns  when  thrust  into  a  jar  of  chlorine.  A 
small  piece  of  the  leaf  is  fastened  to  a  stout  iron  wire  and 
lowered  into  a  250  cc.  cylinder  of  chlorine.  On  entering 
the  gas  the  leaf  takes  fire  and  burns  brilliantly. 
Dutch  metal  leaf  ;  jar  of  CI. 

(6)  A  few  leaves  of  Dutch  metal  are  placed  in  a  dry, 
stout-walled  filter-flask,  which  is  fitted  with  a  one-holed 
rubber  stopper  carrying  a  short  piece  of  rub- 
ber tubing  and  a  pinch-cock.  In  case  the 
filter-flask  has  a  side  tube  it  should  be  securely 
plugged.  The  flask  is  then  attached  to  a 
filter-pump,  and  a  good  vacuum  is  obtained. 
A  glass  tube  is  fastened  to  the  free  end  of 
the  rubber  tube  and  lowered  into  a  500  cc. 
jar  of  chlorine  (Fig  43).  On  opening  the 
pinch-cock  the  chlorine  rushes  up  the  tube 
into  the  flask,  and  the  Dutch  metal  is  imme- 
diately ignited. 

A  straight  glass  stop-cock  may  be  advan- 
tageously used  in  place  of  the  rubber  tube 
and  pinch-cock. 

Filter-flask  ;    rubber  stopper  (1 -holed)  ;   glass  tube  ;    rubber  tube 
and  pinch-cock  ;  Dutch  metal  leaves  ;  jar  of  CI. 


( 

Fig.  43 


HYDROCHLORIC    ACID 

HYDROCHLORIC   ACID 

PREPARATION 


14.  From  the  union  of  hydrogen  and  chlorine.  —  See  Exs. 

7  and  8. 

15.  By  the  combustion  of  chlorine  in  hydrogen.  —  The 

combustion  of  chlorine  in  an  atmosphere  of  hydrogen,  form- 
ing hydrochloric  acid  gas,  may  also  be  shown  by  means  of 
the  apparatus  (Fig.  44). 

Hydrogen  from  a  Kipp  generator  is  conducted  through 
the  cork  in  the  top  of  the  lamp  chimney  and  ignited  at  the 
bottom.  A  regular  stream  of  chlorine,  which  should  not  be 
allowed  to  bubble  through  a  liquid,  is  conducted  through 
the  glass  tube  which  extends  to  the  centre  of  the  cylinder. 
The  tube  is  inserted  in  a  two-holed  rubber 
stopper  which  fits  the  base  of  the  chim- 
ney. As  the  tube  passes  through  the 
hydrogen  flame  the  chlorine  takes  fire 
and  may  be  seen  to  be  burning  at  the 
end  of  the  tube  in  the  atmosphere  of 
hydrogen.  The  cork  is  then  inserted  in 
the  base  of  the  chimney.  The  hydro- 
chloric acid  gas  together  with  the  excess 
of  hydrogen  issues  through  the  open  tube 
(15  cm.  long)  in  the  second  hole  of  the 
cork.  As  the  hydrochloric  acid  gas  comes 
in  contact  with  the  air  it  fumes  strongly. 
By  dipping  the  open  end  of  the  tube  a 
few  millimeters  beneath  the  surface  of  water  in  a  beaker 
the  hydrochloric  acid  will  be  absorbed  and  the  excess  of 
hydrogen  will  bubble  through  the  liquid.  By  carefully 
regulating  the  flow  of  hydrogen  the  minimum  quantity 
may  be  caused  to  escape  uncombined. 


Fig.  44 


90  CHEMICAL   LECTURE   EXPERIMENTS 

It  is  of  the  utmost  importance  in  carrying  out  this  experi- 
ment to  avoid  the  formation  of  an  explosive  mixture  of 
hydrogen  and  chlorine  inside  the  lamp  chimney,  and  conse- 
quently, if  the  flame  of  chlorine  should  be  accidently 
extinguished,  the  current  of  chlorine  should  be  stopped  and 
the  cork  removed,  and,  after  filling  the  lamp  chimney  again 
with  hydrogen,  the  experiment  repeated. 

Apparatus  (Fig.  44)  ;  CI  supply  ;  H  generator  (Kipp). 

16.  Explosion  of  a  mixture  of  hydrogen  and  chlorine  by 
burning  magnesium.  —  The  explosion  of  a  mixture  of  equal 
volumes  of  hydrogen  and  chlorine  may  be  effected  by  the 
actinic  rays  of  a  magnesium  light. 

A  100  cc.  cylinder  is  filled  with  chlorine  and  placed 
mouth  to  mouth  with  a  cylinder  of  equal  size  filled  with 
hydrogen.  The  mixture  of  the  two  gases  must  be  made  by 
diffused  daylight  only  or,  better,  by  gaslight.  The  jars  are 
well  shaken,  separated  by  cardboard  disks,  and  one  of  them 
placed  in  front  of  a  glass  screen.  The  other  should  be 
covered  with  a  towel  or  box  to  cut  out  the  light.  A  strong 
magnesium  flame  is  then  producd  in  front  of  the  screen, 
either  by  allowing  magnesium  powder  to  fall  through  the 
flame  of  a  Bunsen  burner,  or  by  igniting  one  of  the  flash- 
light cartridges  (Ex.  5,  p.  375),  As  a  result  of  the  brilliant 
flash  the  mixture  of  gases  in  the  cylinder  on  the  other  side 
of  the  screen  explodes. 

It  is  important  that  the  gaseous  mixture  should  be 
approximately  correct  as  regards  volume,  and  consequently 
the  chlorine  should  not  be  contaminated  by  too  great  a 
proportion  of  carbon  dioxide,  which  is  likely  to  result  from 
impure  manganese  dioxide.  The  flash  should  be  very  strong 
and  a  considerable  quantity  of  magnesium  must  be  used. 
The  eyes  of  the  operator  should  be  protected  by  colored 
glasses. 


HYDROCHLORIC    ACID  91 

An  interesting  addition  to  the  experiment  may  be  made 
by  interposing  between  the  light  and  the  gases  red  and  blue 
screens.  AVhen  the  red  screen  is  interposed,  no  explosion 
occurs,  as  the  actinic  rays  are  cut  off  by  the  red  glass.  If 
the  blue  screen,  which  permits  the  passage  of  the  actinic 
rays,  is  used,  the  explosion  is  produced. 

H2  +  CI2  =  2  HCl. 

Glass  screen ;  colored  spectacles  ;  Mg  powder  or  flash-light  car- 
tridge ;  100  cc.  cylinder  of  H  ;  100  cc.  cylinder  of  CI. 

17.   By  the  action  of  sulphuric  acid  on  sodium  chloride. — 

Sulphuric  acid  reacts  with  sodium  chloride,  yielding  hydro- 
chloric acid  gas. 

A  constant  current  of  gas  may  be  obtained  by  heating 
120  g.  of  sodium  chloride  with  a  mixture  of  100  cc.  of  con- 
centrated sulphuric  acid  and  60  cc.  of  water.  The  diluted 
acid  must  be  cooled  before  being  introduced  in  the  generat- 
ing flask.  The  apparatus  shown  in  Fig.  39,  p.  81,  is  well 
adapted  for  this  purpose.  The  safety-tube  should  be  half 
filled  with  concentrated  sulphuric  acid  and  the  first  gas 
washing-bottle  with  concentrated  hydrochloric  acid.  By 
means  of  a  three-way  cock  the  gas  can  be  directed  at  will 
either  into  the  flue  or  through  the  sulphuric  acid  in  the  second 
wash-bottle  into  a  piece  of  apparatus.  By  gently' heating 
the  flask  a  regular  current  of  hydrochloric  acid  gas,  which 
is  regulated  by  increasing  or  diminishing  the  size  of  the 
flame,  may  be  obtained.  The  gas  may  be  collected  over 
mercury  or,  owing  to  its  great  specific  gravity,  by  displace- 
ment. 

NaCl  +  H2SO4  =  NaHS04  -f-  HCl. 

Apparatus  (Fig.  39,  p.  81)  ;  NaCl ;  100  cc.  H2SO4  +  60  cc.  H2O 
mixed  and  cooled. 


92 


CHEMICAL   LECTURE   EXPERIMENTS 


Fig.  45 


^  18.  By  the  action  of  concentrated  sulphuric  acid  on  am- 
monium chloride.  —  Concentrated  sulphuric  acid  is  allowed 
to  drop  from  the  funnel  of  the  apparatus 
(Fig.  45)  upon  small  lumps  of  sublimed 
ammonium  chloride  in  the  flask.  The 
issuing  gas  is  conducted  through  a  glass 
elbow  in  the  second  hole  of  the  cork. 

This  method  is  readily  adapted  for 
furnishing  a  large  quantity  of  hydro- 
chloric acid  for  a  considerable  period 
of  time.  In  that  case  it  is  desirable 
to  place  the  lumps  of  ammonium  chlo- 
ride in  the  middle  chamber  of  a  Kipp  generator.  The  acid 
reservoir  is  filled  with  concentrated  sulphuric  acid. 

2  NH4CI  4-  H2SO4  =  (NH4)2S04  +  2  HCl. 

Apparatus  (Fig.  45)  ;  Kipp  generator  (Fig.  17,  p.  46)  ;  lumps  of 
sublimed  NH4CI. 

19.  By  heating  commercial  concentrated  hydrochloric 
acid.  —  Commercial  concentrated  hydrochloric  acid  consists 
of  an  aqueous  solution  of  the  gas.  The  gas  may  be  expelled 
from  the  solution  by  gentle  heat  and,  after  being  dried,  used 
for  any  of  the  experiments  described  beyond.  The  appa- 
ratus (Fig.  39,  p.  81)  is  suitable  for  this  experiment  when  a 
constant  stream  of  the  gas  is  desired.  Two  hundred  cubic 
centimeters  of  the  strongest  acid  are  placed  in  the  generat- 
ing flask,  which  is  then  gently  heated.  A  rapid  evolution  of 
gas  is  obtained. 

The  gas  may  be  made  in  smaller  quantities  by  heating  the 
aqueous  solution  in  a  flask  fitted  with  a  thistle-tube  and  a 
delivery-tube. 


Apparatus   (Fig. 
con.  HCl. 


39,   p.  81)  ;  flask ;   thistle-tube  ;    delivery-tube ; 


HYDROCHLORIC    ACID  93 

20.  By  the  action  of  concentrated  sulphuric  acid  on  ccn- 
centrated  hydrochloric  acid.  —  When  concentrated  sulphuric 
acid  is  allowed  to  fall  upon  concentrated  hydrochloric  acid, 
large  quantities  of  hydrochloric  acid  gas  are  liberated. 

Two  hundred  cubic  centimeters  of  concentrated  commer- 
cial hydrochloric  acid  are  placed  in  a  500  cc.  flask,  fitted 
with  a  two-holed  rubber  stopper  carrying  a  large  dropping- 
funnel  and  a  glass  elbow  (Fig.  45).  Strong  sulphuric  acid  is 
allowed  to  enter,  drop  by  drop,  and  after  a  few  moments 
hydrochloric  acid  gas  will  be  given  off. 

600  cc.  flask  ;  gas  washing-bottle  ;  rubber  stopper  (2-holed) ;  drop- 
ping-funnel ;  elbow. 

PROPERTIES 

21.  Generation  of  heat  by  the  absorption  of  the  gas  in 
water.  —  The  absorption  of  hydrochloric  acid  gas  by  water 
is  accompanied  by  a  great  evolution  of  heat. 

The  bulb  of  a  thermometer  is  covered  with  a  piece  of 
filter-paper  moistened  with  water.  If  the  thermometer  is 
thrust  into  a  jar  of  the  gas,  the  water  on  the  filter-paper 
absorbs  sufficient  gas  with  generation  of  heat  to  cause  the 
mercury  to  rise  in  the  thermometer  some  40  to  50  degrees. 

The  ether  thermometer  described  in  Ex.  73,  p.  174,  may 
here  be  used  to  advantage.  The  bulb,  which  is  about  one- 
third  filled  with  ether,  is  wrapped  with  a  wet  filter-paper, 
and  the  thermometer  then  thrust  into  a  cylinder  of  the  gas. 
Sufficient  heat  is  generated  to  boil  the  ether.  The  ether 
vapor  issuing  from  the  end  of  the  tube  may  be  ignited. 

Thermometer;  ether  thermometer  (Ex.  73,  p.  174);  ether;  2  cyl- 
inders of  dry  HCl. 

22.  Solubility  in  water.  —  Water  dissolves  450  volumes 
of  hydrochloric  acid  gas  at  the  ordinary  temperature. 

A  dry  cylinder  filled  with  the  gas  is  covered  with  a  metal 
plate  and  opened  under  water.     As  the  plate  is  slipped  to 


L^ 


94        CHEMICAL  LECTURE  EXPERIMENTS 

one  side,  the  water  rushes  with  almost  explosive  violence 
into  the  cylinder,  filling  the  interior. 

The  absorption  of  the  gas  in  water  with  the  production  of 
a  fountain  may  be  shown  by  means  of  the  apparatus  (Fig. 
84,  p.  195).  The  large  flask  is  filled  with  dry  hydrochloric 
acid  gas  by  downward  displacement,  and  after  the  cork 
carrying  the  long  glass  tube  and  small  pipette  nearly  filled 
with  water  has  been  inserted,  is  firmly  supported  in  an  in- 
verted position.  The  long  glass  tube  is  dipped  under  water 
colored  blue  with  litmus  solution.  On  pinching  the  rubber 
bulb  of  the  pipette  the  operation  is  started,  and  the  water 
rushes  with  great  force  through  the  long  tube  into  the  flask. 
The  litmus  solution  is  turned  to  a  deep  red  by  the  acid. 

Apparatus  (Fig.  84,  p.  195)  ;  large  flask  (dry)  ;  rubber  bulb  pipette 
(medicine  dropper  or  ink  filler)  ;  HCl  supply;  litmus  solution. 

23.  Preparation  of  aqueous  hydrochloric  acid.  —  The  prep- 
aration of  aqueous  hydrochloric  acid  on  a  large  scale  may 
be  accomplished  by  conducting  the  gas  through  a  series  of 
Wolff  bottles  (Fig.  85,  p.  196),  provided  with  safety-tubes. 
The  arrangement  of  the  bottles  is  identical  with  that  de- 
scribed for  preparing  ammonium  hydroxide,  with  the  single 
exception  that  the  tubes  conducting  the  gas  into  the  dilfer- 
ejit  bottles  dip  only  a  few  millimeters  beneath  the  surface 
of  the  water. 

As  the  absorption  proceeds,  currents  of  the  heavy  aqueous 
hydrochloric  acid  may  be  seen  to  be  settling  in  the  liquid  in 
the  Wolff  bottles. 

Series  of  Wolff  bottles  (Fig.  85,  p.  196) ;  HCl  supply. 

24.  Electrolysis  of  hydrochloric  acid.  —  The  decomposi- 
tion of  aqueous  hydrochloric  acid  by  the  electric  current  into 
equal  volumes  of  chlorine  and  hydrogen  is  at  best  an  unsatis- 
factory experiment.     While  the  products  of  the  decompo- 


HYDROCHLORIC   ACID 


96 


sition  of  water,  i.e.,  hydrogen  and  oxygen,  are,  relatively 
speaking,  insoluble  in  water,  chlorine  is  very  soluble,  and 
it  becomes  necessary  to  continue  the  electrolysis  until  the 
liquid  is  saturated  with  chlorine. 

The  electrolytic  apparatus  (Fig. 
46)  is  provided  with  carbon  elec- 
trodes, consisting  of  rods  of  elec- 
tric-light carbon,  preferably  of  a 
small  size,  inserted  in  rubber  stop- 
pers. Platinum  electrodes,  when 
used  for  this  decomposition,  are  at- 
tacked by  the  nascent  chlorine. 

The  addition  of  small  quantities 
of  sodium  chloride  to  the  hydro- 
chloric acid  used  in  the  experiment 
diminishes  the  capacity  of  the  liquid 
for  the  absorption  of  chlorine.  Con- 
centrated hydrochloric  acid  is  satu- 
rated with  sodium  chloride  and  the 
saturated  liquid  used  in  the  elec- 
trolytic apparatus.  Both  stop-cocks 
being  open,  sufficient  acid  is  poured 
into  the  bulb  to  rise  in  the  two  arms 
to  within  2  cm.  of  the  stop-cocks. 
The  current  from  six  cells  of  a  bi- 
chromate battery  is  then  conducted 
through  the  liquid  for  half  an  hour, 
leaving  the  stop-cocks  open.  While 
this  operation  as  a  rule  should  be  be- 
gun before  the  lecture,  the  difference 

in  the  evolution  of  gases  from  the  two  poles  forms  an  inter- 
esting experiment  for  showing  the  solubility  of  chlorine. 
At  the  end  of  half  an  hour  the  liquid  in  the  arm  of  the 
electrolytic  apparatus  over  the  positive  electrode  will  have 


Fig.  46 


96  CHEMICAL   LECTURE   EXPERIMENTS 

become  saturated  with  chlorine,  and  by  closing  both  stop- 
cocks it  will  be  found  that  the  two  tubes  fill  with  gas  at 
nearly  the  same  rate.  The  volume  of  hydrogen  will  proba- 
bly be  somewhat  greater  than  that  of  chlorine,  though  if  the 
stop-cock  is  carefully  opened  and  the  liquid  allowed  to  rise 
in  the  hydrogen  tube  to  the  level  of  the  liquid  in  the  chlo- 
rine tube,  after  20  or  30  cc.  of  gas  have  collected,  the  vol- 
umes of  the  gases  will  increase  with  much  greater  regularity. 
Rubber  rings  are  advantageously  placed  on  the  arms  about 
15  cm.  below  the  stop-cocks,  and  the  actual  measurement  of 
the  evolution  of  the  gases  begun  when  the  liquids  have  been 
depressed  to  this  level. 

A  piece  of  white  paper  held  behind  the  tube  containing 
chlorine  will  show  the  green  color  of  the  gas.  On  opening 
the  stop-cock  the  hydrogen  may  be  ignited  as  it  issues  from 
the  tube,  and  a  piece  of  iodo-starch  paper  is  instantly  turned 
blue  when  held  in  the  gas  issuing  from  the  other  stop-cock. 

2HC1  =  H2  +  Cl2. 

Electrolytic  apparatus  (Fig  46)  ;  carbon  electrodes ;  bichromate 
battery  ;  HCl  saturated  with  NaCl ;  Kl-starch  paper. 

25.  The  electrolysis  of  hydrochloric  acid  and  the  collection 
of  the  mixture  of  hydrogen  and  chlorine.  —  The  explosive 
mixture  of  hydrogen  and  chlorine  is  most  satisfactorily 
obtained  from  the  electrolysis  of  hydrochloric  acid,  and  the 
mixture  so  formed  is  considerably  more  sensitive  to  the 
actinic  rays  of  light  than  the  mechanical  mixture  made  in 
Ex.  16. 

The  hydrochloric  acid  is  best  decomposed  in  an  electro- 
lytic apparatus  like  that  shown  in  Fig.  47.  Owing .  to 
the  corrosive  action  of  nascent  chlorine  on  platinum,  it  is 
necessary  to  use  carbon  electrodes.  This  may  be  done 
either   by   thrusting   small   rods   of    electric   light  carbon 


HYDROCHLORIC    ACID 


97 


r^f^ 

L 

=11 

,      l" 

=:=-..= 

r^ 

i  l  =-~ 

- 

B!^ 

—  ,,r 

=^  ^= 

E^3 

Fig.  47 


through  the  holes  of  a  cork,  or,  in  case  rods  of  small 
diameter  are  not  available,  pieces  of  carbon  of  the  regular 
size  may  be  fastened  to  platiimm  wires  sealed  into  the  glass 
tubes,  which  are  filled  with  mercury  as  indicated.  Inasmuch 
as  here  again  the  liquid  being  electro- 
lyzed  should  be  completely  saturated 
with  chlorine,  the  minimum  quantity 
of  acid  should  be  used  and  a  bottle 
should  be  selected  just  large  enough 
to  take  the  cork  conveniently  and  not 
have  the  electrodes  touch.  Concen- 
trated hydrochloric  acid,  saturated  with 
salt  as  described  in  the  preceding  ex- 
periment, is  poured  into  the  bottle  to 
within  2  cm.  of  the  cork.  Owing  to  the  rise  in  tempera- 
ture attending  the  electrolysis,  it  is  advisable  to  place  the 
bottle  in  a  crystallizing  dish  containing  cold  water.  The 
room  is  darkened  so  as  to  have  very  diffused  daylight,  or 
better  only  gaslight,  and  then  the  apparatus  is  connected 
with  six  cells  of  the  bichromate  battery.  The  evolution  of 
gas  begins  almost  immediately,  though,  as  the  major  part 
of  the  chlorine  is  absorbed  by  the  acid  in  the  bottle,  the 
first  portions  of  the  gas  consist  mainly  of  hydrogen.  After 
the  apparatus  has  been  running  for  half  an  hour  the  mixed 
gases  may  be  collected  over  salt  brine.  Several  small  cyl- 
inders and  the  lecture  eudiometer  (T'ig.  11,  p.  26)  should 
be  filled  with  the  gas. 

At  the  conclusion  of  the  experiment  the  current  is  stopped, 
and  before  exposing  the  apparatus  to  bright  light,  the  excess 
of  the  explosive  gaseous  mixture  remaining  in  the  bottle 
above  the  liquid  should  be  removed  by  taking  out  the 
cork. 

The  cylinders  of  the  mixed  gases  may  be  exploded  either 
by  a  match  or  by  means  of  the  magnesium  light  (Ex.  16). 


98  CHEMICAL   LECTURE   EXPERIMENTS 

The  gas  in  the  lecture  eudiometer  is  reserved  for  use  in 
the  following  experiment. 

Electrolytic  apparatus  consisting  of  small  wide-mouthed  bottle,  3- 
holed  cork,  and  carbon  electrodes  (Fig.  47)  ;  bichromate  battery  ; 
eudiometer  (Fig.  11,  p.  26)  ;  salt  brine  ;  HCl  saturated  with  NaCl. 

26.  Analysis  of  the  mixture  of  hydrogen  and  chlorine 
obtained  by  the  electrolysis  of  hydrochloric  acid.  —  That  the 
gas  in  the  lecture  eudiometer  from  the  preceding  experiment 
consists  of  a  mixture  of  equal  volumes  of  hydrogen  and 
chlorine  is  shown  by  allowing  a  strong  solution  of  potassium 
iodide  to  flow  through  the  stop-cock  into  the  gas.  The 
solution  immediately  becomes  dark-colored  from  the  libera- 
tion of  iodine,  and  the  liquid  will  rise  inside  the  tube  half- 
way to  the  stop-cock.  If  the  eudiometer  is  then  inverted 
and  the  residual  gas  tested,  it  will  be  found  to  burn  quietly, 
giving  the  hydrogen  flame. 

Eudiometer  filled  with  H  and  CI  from  the  preceding  experiment ; 
KI  solution. 

CHLORINE   MONOXIDE 

27.  Preparation.  —  When  chlorine  is  passed  over  yellow 
mercuric  oxide,  the  brownish  oxychloride   of  mercury  to- 
gether with  chlorine   monoxide 
is  formed. 

A  slow  stream  of  chlorine  is 


■■\^■^li^»^>,■Avi>1>^Vn^S?.^r — i-a — vN  -III  1  ■  r>         1 

passed  through  a  piece  oi  glass 
tubing,   50   cm.   long   and   8   to 
10  mm.  internal  diameter,  which 
Fig.  48  is  bent  at  right  angles  at  a  dis- 

tance of  10  cm.  from  one  end 
(Fig.  48).  Dry  mercuric  oxide  (the  yellow  amorphous 
modification)  is  placed  in  the  tube,  which  is  clamped  in  a 
horizontal  position,  the  elbow  dipping  into  a  small  cylin- 


HYPOCHLOROUS   ACID  99 

der.  That  portion  of  the  tube  containing  the  mercuric  oxide 
is  kept  cool  by  allowing  ice- water  to  drop  on  a  piece  of  filter- 
paper  laid  upon  it.  In  a  few  minutes  the  cylinder  will  be 
filled  with  a  brownish  yellow  gas.  Several  cylinders  of  the 
same  size  should  be  filled. 

A  small  quantity  of  chlorine  monoxide  is  exploded  by 
thrusting  a  burning  match  or  hot  iron  wire  into  the  mouth 
of  a  cylinder. 

Sulphur  flowers  are  sifted  into  a  cylinder  of  chlorine  mo- 
noxide.    The  reaction  follows  with  an  explosion. 

A  2  or  3  mm.  piece  of  phosphorus  placed  in  a  small 
deflagrating  spoon  is  lowered  into  a  jar  of  the  gas.  An  ex- 
plosion takes  place. 

Glass  tube  50  cm.  long,  8-10  mm.  internal  diameter;  several  small 
cylinders  ;  ice-water  ;  CI  generator;  HgO  (yellow)  ;  S  flowers  ;  P. 

HYPOCHLOROUS     ACID 

PREPARATION 

28.  By  the  action  of  chlorine  on  mercuric  oxide.  —  Moist, 
freshly  precipitated  mercuric  oxide  is  covered  with  strong 
chlorine  water.  The  oxide  soon  dissolves,  forming  a  solu- 
tion of  hypochlorous  acid. 

Yellow  mercuric  oxide  may  be  suspended  in  water  in  a 
200  cc.  flask  and  chlorine  conducted  into  the  liquid.  The 
brown  oxychloride  is  soon  formed  and  a  considerable  quantity 
of  mercuric  oxide  goes  into  solution.  The  clear  filtrate  con- 
tains hypochlorous  acid. 

HgO  +  H2O  +  2CI2  =  HgClg  +  2HC10     [?]. 

200  cc.  flask  ;  CI  water  or  CI  generator;  HgO  (freshly  precipitated). 

29.  By  the  action  of  nitric  acid  on  calcium  hypochlorite. — 

If  a  5  per  cent  solution  of  nitric  acid  is  carefully  added  to  a 
clear  solution  of  calcium  hypochlorite,  a  liquid  containing 


100 


CHEMICAL   LECTURE   EXPERIMENTS 


calcium  nitrate,  calcium  chloride,  and  hypochlorous  acid  is 
obtained  which  by  distillation  yields  a  colorless  solution  of 
hypochlorous  acid. 

Bleaching  powder  solution ;    5  per  cent  HNO3. 

30.  Preparation  of  chloride  of  lime.  —  (a)  By  conducting 
chlorine  over  moistened  calcium  hydroxide  a  mixture  of 
calcium  hypochlorite  and  calcium  chloride,  the  so-called 
chloride  of  lime,  is  formed. 

A  40  cm.  length  of  combustion  tubing  is  filled  with  cal- 
cium hydroxide  which  is  slightly  moistened.  A  current  of 
chlorine,  passed  through  a  gas  washing-bottle  containing 
water,  is  conducted  into  one  end  of  the  tube  and  a  cork 


"^ 


fgaag.gSg'it^g: 


'^Ec^g^.        dl 


Fig.  49 


carrying  a  glass  elbow  dipping  into  a  beaker  of  water  is 
thrust  into  the  other  end  (Fig.  49).  On  account  of  the 
absorption  of  the  chlorine  by  the  calcium  hydroxide,  very 
little  if  any  chlorine  leaves  the  tube. 

Apparatus  (Fig.  49)  ;  40  cm.  length  of  combustion  tubing  ;  gas 
washing-bottle  ;  CI  generator  ;  Ca(0H)2. 

(b)  A  2  1.  flask  is  filled  with  chlorine  and  about  20  cc. 
of  the  milk  of  lime  are  introduced.  On  shaking  the  flask 
the  chlorine  is  entirely  absorbed,  as  may  be  noticed  by  the 


CHLORINJi: '  PE??10XIIXHJ'  101 

disappearance  of  the  green  color.  On  the  addition  of  an 
excess  of  concentrated  hydrochloric  acid,  chlorine  is  liberated 
and  the  flask  again  becomes  filled  with  the  green  gas. 

2  1.  flask  ;  CI  generator  ;  milk  of  lime. 

31 .  Bleaching  action  of  sodium  hypochlorite.  —  Sodium 
hypochlorite  bleaches  colored  cloth  (turkey  red).  A  small 
piece  of  the  cloth  is  dipped  into  a  solution  of  sodium  hypo- 
chlorite in  a  beaker.  In  a  few  moments  the  color  will 
disappear. 

If  hypochlorous  acid  is  present,  the  bleaching  is  more 
rapid,  and  consequently  if  a  small  quantity  of  hydrochloric 
acid  is  added  to  the  sodium  hypochlorite  in  a  second  beaker, 
a  piece  of  cloth  dipped  in  the  liquid  is  almost  immediately 
bleached. 

Sodium  hypochlorite  ;  cloth  dyed  turkey  red. 

32.  Action  of  hypochlorous  acid  on  silver  oxide.  —  Silver 
oxide  and  hypochlorous  acid  interact,  forming  silver  chloride 
and  liberating  oxygen. 

A  few  grams  of  the  oxide  are  placed  in  a  test-tube  and 
covered  with  a  strong  solution  of  hypochlorous  acid.  On 
gently  warming,  a  gas  will  be  evolved  which  when  tested  is 
seen  to  be  oxygen. 

The  experiment  may  be  repeated,  using  cupric  oxide  and 
a  solution  of  bleaching  powder. 

2  HCIO  -f-  AgsO  =  2  AgCl  +  H^O  +  0,. 

HCIO  solution  ;  Ag20  ;  fresh  bleaching  powder  ;  CuO. 

CHLORINE    PEROXIDE 

33.  Preparation. — A  few  centigrams  of  finely  powdered 
potassium  chlorate  are  placed  in  a  crucible  which  rests  on 
the  bottom  of  a  100  cc.  cylinder.     Five  drops  of  concentrated 


102 


fcHSMJCTAt  liiECJ^UKE   EXPERIMENTS 


<^ 


Fia.  50 


sulphuric  acid  are  allowed  to  fall,  one  at  a  time,  upon  the 
potassium  chlorate  from  a  long  glass  tube  bent  at  one  end. 
A  yellowish  gas  is  slowly  evolved  and  displaces  the  air  in 

the  cylinder.  When  a  long  iron 
wire  is  heated  at  one  end  and 
lowered  into  the  gas,  a  sharp 
explosion  takes  place,  and  care 
should  be  taken  to  protect  the 
face  and  hands  from  flying  drops 
of  acid  (Fig.  50). 

In  preparing  chlorine  peroxide 
the  potassium  chlorate  may  be 
allowed  to  fall  into  sulphuric 
acid.  Two  or  three  cubic  centimeters  of  strong  sulphuric 
acid  are  placed  in  the  bottom  of  a  small  thick-walled  glass 
cylinder  and  2  g.  of  potassium  chlorate  are  carefully  sifted 
into  the  acid,  care  being  taken  to  protect  the  hand  with  a 
gauntlet.  The  yellow  gas  rises  in  the  cylinder  and  may  be 
exploded  with  an  iron  wire. 

Two  100  cc.  stout- walled  cylinders  ;  crucible  ;  bent  glass  tube  ;  glass 
shield  ;  gauntlets  ;  iron  wire  ;  KCIO3. 

34.   Action  of  hydrochloric  acid  on  potassium  chlorate.  — 

A  concentrated  solution  of  potassium  chlorate,  when  heated 
with  concentrated  hydrochloric  acid,  turns  yellow,  and  the 
gas  evolved  bleaches  litmus  paper. 

If  a  hot  glass  rod  is  held  in  the  gas  from  the  test-tube,  a 
slight  explosion  follows. 

On  the  powdered  salt  the  action  of  the  acid  is  more 
marked,  producing  the  mixture  of  chlorine  and  chlorine 
dioxide  called  "  euchlorine." 


35.    Chlorine   peroxide    and    sugar. — Equal    weights   of 
finely  pulverized  potassium  chlorate  and   cane   sugar   are 


CHLORINE    PEROXIDE  103 

carefully  mixed  on  paper,  avoiding  all  friction,  and  placed 
on  an  asbestos  sheet  or  a  brick  in  a  hood.  One  drop  of 
sulphuric  acid  is  allowed  to  come  in  contact  with  the  mix- 
ture, which  is  ignited  and  burns  fiercely.  The  sulphuric 
acid  may  be  dropped  from  a  long  bent  glass  tube,  or  the 
acid  may  be  more  satisfactorily  added  by  dropping  a  small 
piece  of  asbestos  paper  in  concentrated  sulphuric  acid  and 
allowing  the  moistened  paper  to  fall  on  the  powdered  mix- 
ture. The  combustion  proceeds  with  great  rapidity,  giving 
an  intense  blue  potassium  flame. 

Asbestos  sheet ;  KCIO3;  sugar. 

36.  Combustion   of    phosphorus.  —  Phosphorus    burns   in 
chlorine  peroxide,   and   the  combustion   may  be 
made  to  proceed  under  water. 

Five  grams  of  crystallized  potassium  chlorate 
are  placed  on  the  bottom  of  a  100  cc.  cylinder  or, 
better,  of  a  test-tube  on  foot  (Fig.  51).  Fifty 
cubic  centimeters  of  water  are  then  added  and 
two  or  three  2  mm.  pieces  of  phosphorus  are 
thrown  into  the  water. 

A  10  cc.  pipette  is  half  filled  with  concentrated 
sulphuric  acid  and  the  tip  thrust  into  the  cylinder       „      _. 
until  it  touches  the  potassium  chlorate  crystals. 
As  the  acid  comes  in  contact  with  the  crystals,  chlorine 
peroxide  is  evolved  and  the  phosphorus  burns. 

Test-tube  on  foot  (Fig.  51)  ;  10  cc.  pipette  ;  crystallized  KCIO3; 
2  mm.  pieces  of  P. 

37.  Explosive  combustion  of  alcohol  in  chlorine  per- 
oxide.—  A  small  quantity  of  chlorine  peroxide  is  generated 
in  a  50  cc.  cylinder  according  to  the  method  in  Ex.  33.  The 
cylinder  is  placed  behind  a  glass  screen  and  a  few  drops  of 
alcohol  are  allowed  to  fall  from  a  test-tube  into  the  gaseous 


104  CHEMICAL  LECTURE   EXPERIMENTS 

mixture.     A  sharp  explosion  occurs  which  is  likely  to  blow 
some  of  the  acid  out  of  the  cylinder. 

Glass  screen  ;  alcohol ;  CIO2  in  cylinder. 

CHLORIC   ACID 

38.  Preparation.  —  Sulphuric  acid,  when  added  to  a  solu- 
tion of  barium  chlorate,  forms  barium  sulphate  and  chloric 
acid. 

Dilute  sulphuric  acid  should  be  gradually  added  to  a  solu- 
tion of  barium  chlorate  until  the  barium  is  completely  pre- 
cipitated. On  filtering  off  the  liquid  it  will  be  found  to 
contain  chloric  acid  and  possess  strong  bleaching  properties. 

Ba(C103)2  +  H2SO,  =  BaS04  +  2  HCIO3. 

Litmus;  Ba(C103)2. 

PERCHLORIC   ACID 

39.  Preparation.  —  Sulphuric  acid  reacts  with  pure  potas- 
sium perchlorate,  liberating  perchloric  acid. 

Five  grams  of  chemically  pure 
potassium  perchlorate  are  heated 
gently  with  12  cc.  of  pure  concen- 
trated sulphuric  acid  in  a  100  cc. 
tubulated  retort  (Fig.  52).  The 
powder  is  placed  in  the  flask  and  the 
.  X .         concentrated  acid  poured   through 

1  ^^     a  funnel,  the   introduction  of  acid 

cgft  ^H     i^ito  the  neck  of  the  retort  being 

YiQ,  52  thus  avoided.      The  retort  is  then 

gently  heated  by  a  low  flame.  A 
high  temperature  is  as  undesirable  as  it  is  unnecessary, 
since  the  perchloric  acid  distils  at  about  110°.    A  few  drops 


PERCHLORIC    ACID  105 

of  an  oily,  strongly  fuming  distillate  are  obtained  in  the 
test-tube  used  as  a  receiver. 

2  KCIO4  +  H2SO4  =  K2SO4  +  2  HCIO4. 
100  cc.  tubulated  retort ;  c.  p.  KCIO4  ;  c.  p.  con.  H2SO4. 

40.  Bleaching  action.  —  One  drop  of  the  distillate  ob- 
tained in  the  preceding  experiment  is  allowed  to  fall  into  a 
test-tube  containing  3  or  4  cc.  of  water.  The  diluted  per- 
chloric acid,  when  added  to  a  solution  of  indigo,  bleaches  it 
immediately. 

Perchloric  acid ;  indigo  solution. 

41.  Combustion  of  charcoal.  — Perchloric  acid  is  a  strong 
oxidizing  agent,  and  when  a  small  piece  of  charcoal,  heated 
to  glowing,  is  dropped  into  a  test-tube  containing  a  few 
drops  of  the  acid,  the  charcoal  bums. 

Perchloric  acid ;  charcoal. 

24.  Action  on  organic  matter. — A  drop  of  perchloric  acid 
on  the  end  of  a  glass  rod  is  spread  on  a  piece  of  filter-paper. 
The  acid  destroys  the  paper  completely,  cutting  a  hole  in  it 
and  igniting  it.  By  holding  the  paper  high  above  the  flame 
and  gently  warming  it  the  ignition  may  be  immediately  ac- 
complished. 

A  drop  of  the  perchloric  acid  is  spread  on  the  stem  of  a 
match  held  with  pincers.  The  match  is  lighted,  and  when 
the  flame  reaches  the  part  covered  with  acid,  the  combustion 
is  much  more  rapid,  and  the  flame  sputters. 


BROMINE 


BROMINE 


1.  Preparation  from  potassium  bromide.  —  Metallic  bro- 
mides, when  heated  with  sulphuric  acid  in  the  presence  of 
an  oxidizing  agent  such  as  manganese  dioxide,  give  up  all 
their  bromine.  This  reaction,  used  in  the  technical  prepa- 
ration of  the  element,  is  easily  carried  out  on  a  small  scale. 

Three  and  one-half  grams  of  powdered  potassium  bromide 
are  mixed  with  7  g.  of  finely  pulverized  manganese  dioxide 
and  introduced  into  a  500  cc.  retort.  Fifteen  cubic  centi- 
meters of  concentrated  sulphuric  acid  and  90  cc.  of  water  are 
mixed  and  carefully  introduced,  care  being  taken  to  get  none 
of  the  acid  into  the  neck  of  the  retort.  After  the  mixture  is 
thoroughly  stirred  the  retort  is  placed  on  a  ring-stand  and  its 
neck  thrust  deep  into  a  500  cc.  flask,  which  can  be  externally 
cooled  by  immersion  in  water.  On  gently  heating  the  con- 
tents of  the  retort  the  bromine  is  liberated,  filling  the  retort 
with  deep  reddish  brown  fumes,  which  distil  over  and  con- 
dense in  the  flask  to  a  heavy,  dark  fluid,  bromine,  covered 
with  a  lighter  layer  of  bromine  water.  Owing  to  the  vola- 
tility of  the  bromine  the  flask  should  be  cooled  with  ice- 
water.     (Fig.  93,  p.  223.) 

2  KBr  4-  MnOa  +  2  H2SO4  =  K2SO4  -f-  MnS04  +  2  HgO  +  Br2. 

500  cc.  retort ;  500  cc.  flask  ;  ice-water ;  KBr  ;  MUO2. 

106 


BROMINE     >  107 

2.  Solidification  by  cold.  —  Bromine  readily  freezes  in  a 
mixture  of  salt  and  ice  to  a  dark,  crystalline  mass  which  has 
a  dull  metallic  lustre.  Five  cubic  centimeters  of  bromine 
are  placed  in  a  thin-walled  test-tube  and  immersed  in  a  freez- 
ing-mixture of  salt  and  ice.  After  a  few  minutes  the  bro- 
mine will  have  solidified.  The  tube  is  warmed  a  little  in  the 
hand,  and  the  solid  lump  of  bromine  still  retaining  the  shape 
of  the  test-tube  shaken  out  upon  a  white  plate^ 

Ice  and  salt ;  Br. 

3.  Vaporization.  —  Bromine  is  very  volatile,  giving  rise 
to  a  deep  reddish  brown  vapor.  This  is  best  shown  by  pour- 
ing 5  drops  of  liquid  bromine  into  a  dry  500  cc.  flask,  the 
mouth  of  which  is  covered  with  a  small  watch-glass.  On 
gently  warming,  the  vapor  rises,  displacing  the  air,  and  fills 
the  flask  with  deep-colored  fumes. 

600  cc.  flask  ;  watch-glass  ;  Br. 

4.  Bromine  water.  —  Five  cubic  centimeters  of  bromine 
are  poured  into  200  cc.  of  water  in  a  250  cc.  flask.  The 
bromine,  by  reason  of  its  great  specific  gravity,  sinks  to  the 
bottom  of  the  flask.  On  corking  the  flask  and  shaking,  the 
bromine  is  dissolved  in  the  water. 

5.  Action  on  arsenic  and  antimony.  —  When  either  anti- 
mony or  arsenic  is  allowed  to  come  in  contact  with  liquid 
bromine,  a  vigorous  reaction  occurs,  the  metal  burning  on  top 
of  the  bromine. 

One  cubic  centimeter  of  liquid  bromine  is  placed  in  a  test- 
tube  which  is  inserted  in  the  mouth  of  a  wide-mouthed  bot- 
tle (Fig.  109,  p.  262).  A  2  or  3  mm.  piece  of  antimony  or 
arsenic  is  dropped  into  the  liquid.  In  case  the  heat  is  suf- 
ficient to  break  the  tube,  the  bromine  will  fall  into  the  wide- 
mouthed  bottle  and  there  do  no  harm. 

Apparatus  (Fig.  109,  p.  262);  As  ;  Sb  ;  Br. 


108 


CHEMICAL   LECTURE   EXPERIMENTS 


HYDROBROMIC   ACID 


H;j=2i< 


nil 


FORMATION  AND  PREPARATION 

6.   By  heating  a  mixture  of  hydrogen  and  bromine.  —  If 

hydrogen  is  allowed  to  bubble  through  bromine  and  is  then 
ignited,  sufficient  bromine  vapor  will 
have  been  carried  with  the  hydrogen 
to  combine  with  it  and  form  hydro- 
bromic  acid. 

A  simple  arrangement  for  this  ex- 
periment consists  of  a  large  test-tube 
fitted  with  a  two-holed  rubber  stopper. 
Hydrogen  is  allowed  to  pass  through  a 
glass  elbow  thrust  through  the  stopper 
down  to  the  bottom  of  the  test-tube  in 
which  a  few  drops  of  bromine  are  placed. 
An  open  glass  tube  is  thrust  through 
the  other  hole  in  the  cork  and.  serves 
as  a  jet.  After  sufficient  hydrogen  has 
passed  through  the  apparatus  to  drive 
^  out  all  air,  the  gas  is  lighted  at  the 
open  tube.  Clouds  of  hydrobromic  acid 
vapor  will  appear,  the  quantity  of  which 

may  be  increased  by  gently  warming  the  bromine  in  the 

test-tube  (Fig.  53). 
H  generator  ;  Br. 


Fig.  53 


7.  By  the  action  of  bromine  on  hydrogen  sulphide.  —  Bro- 
mine unites  with  the  hydrogen  of  hydrogen  sulphide,  form- 
ing hydrobromic  acid  and  setting  free  sulphur.  By  filtering 
off  the  sulphur  a  dilute  solution  of  hydrobromic  acid  may  be 
obtained. 

Hydrogen  sulphide  gas  is  conducted  into  a  100  cc.  Erlen- 
meyer  flask  containing  20  cc.  of  strong  bromine  water.     In  a 


HYDllOBROMIC    ACID 


109 


few  minutes  the  solution  will  have  become  decolorized  and 
large  quantities  of  sulphur  will  have  separated.  By  adding 
a  few  more  drops  of  bromine  from  time  to  time,  the  reaction 
may  be  continued. 

HgS-f  Br2  =  2HBr  +  S. 
100  cc.  flask  ;  H2S  generator  ;  Br  water. 

8.  From  sulphuric  acid  and  potassium  bromide.  —  Dilute 
sulphuric  acid  liberates  hydrobromic  acid  from  bromides 
in  a  pure  form  containing  but  small  quantities  of  bromine 
vapor  or  sulphur  dioxide.  This  method  is  very  satisfactory 
for  the  preparation  of  gaseous  hydrobromic  acid. 

Ten  grams  of  potassium  bromide  are  placed  in  a  300  cc. 
Erlenmeyer  flask  fitted  with  a  dropping-funnel  and  a  glass 
elbow  (Fig.  54) .  A  mixture  ism  ade 
of  3  volumes  of  concentrated  sul- 
phuric acid  and  1  volume  of  water 
by  pouring  the  acid  gradually  into 
the  water  and  cooling  the  mixture. 
Sufficient  of  this  mixture  is  added 
to  cover  the  potassium  bromide 
and  the  contents  of  the  flask  are 
very  gently  warmed.  The  gas  is 
steadily  evolved  and  may  be  col- 
lected in  cylinders  by  displace- 
ment.   The  gas  regulation  is  easily 

controlled  by  varying  the  heat  applied  to  the  flask.  If  the  gas 
is  not  perfectly  colorless,  the  small  quantity  of  bromine  vapor 
may  be  removed  by  conducting  the  gas  through  a  U-tube  filled 
either  with  red  phosphorus  or  with  glass  beads  or  pumice- 
stone  drenched  with  concentrated  hydrobromic  acid  solution. 

2  KBr  -f  H2SO4  =  K2SO4  +  2  HBr. 

300  cc.  Erlenmeyer  flask  ;  dropping-funnel ;  KBr  ;  H2SO4  (3  : 1)  ; 
U-tube  ;  red  P ;  con.  HBr  solution. 


Fig.  54 


110 


CHEMICAL  LECTURE  EXPERIMENTS 


9.  From  bromine  and  naphthaline.  —  Bromine  reacts  with 
naphthaline,  liberating  hydrobromic  acid  gas.  This  reaction 
is  very  satisfactory  for  preparing  the  gas. 

Fifteen  grams  of  naphthaline  are  covered  with  20  cc.  of 
kerosene  in  a  500  cc.  distilling  flask.  A  small  dropping- 
funnel,  the  tip  of  which  should  dip  beneath  the  liquid,  is 
inserted  in  a  one-holed  stopper  in  the  neck  of  the  flask  (Fig. 
55).  Fifteen  to  20  cc.  of  bromine  are  placed  in  the  drop- 
ping-funnel  and  allowed  to  flow  very  slowly  into  the  flask. 
The  reaction   begins  almost  immediately,  and  the  hydro- 


FiG.  55 


bromic  acid  gas,  which  carries  with  it  slight  traces  of  bro- 
mine vapor,  should  be  purified  by  conducting  it  through 
a  gas  washing-bottle  containing  not  more  than  10  cc.  of  a 
strong  aqueous  solution  of  hydrobromic  acid  in  which  a 
small  quantity  of  red  phosphorus  is  suspended.  The  issu- 
ing gas  will  be  perfectly  colorless.  While  the  heat  of  the 
reaction  is  often  sulficient  to  liberate  the  hydrobromic  acid 
gas,  the  flask  may  advantageously  be  very  gently  warmed 
with  a  low,  smoky  flame.  The  gas  washing-bottle  may  be 
replaced  by  a  U-tube  filled  with  red  phosphorus.     The  puri- 


HYDROBROMIC    ACID  111 

fied  gas  is  dried  by  conducting  it  through  a  tube  containing 
calcium  chloride. 

500  cc.  distilling  flask  ;  100  cc.  dropping-funnel ;  gas  washing-bottle  ; 
CaCla  drying-tube  ;  U-tube  containing  red  P  ;  naphthaline  ;  Br ;  kero- 
sene ;  red  P  ;  con.  HBr. 

PROPERTIES 

10.  Hygroscopic  nature.  —  On  opening  a  cylinder  of  hydro- 
bromic  acid  the  gas  fumes  in  the  air. 

11.  Action  with  litmus.  —  A  piece  of  moistened  blue  lit- 
mus paper  thrust  into  a  jar  of  the  gas  will  be  reddened. 

12.  Action  with  ammonia.  —  A  few  drops  of  strong  am- 
monium hydroxide  are  poured  on  a  test-tube  brush,  which  is 
then  lowered  into  a  jar  of  the  gas.  Dense  white  fumes  of 
ammonium  bromide  are  formed. 

13.  Solubility  in  water.  —  A  jar  of  gaseous  hydrobromic 
acid  is  opened  under  water.  The  solubility  is  so  great  that 
the  water  rushes  into  the  cylinder  with  considerable  violence. 

14.  Decomposition  by  chlorine.  —  Two  cylinders  of  equal 
size  are  filled,  one  with  hydrobromic  acid  gas,  and  the  other 
with  chlorine.  The  cylinder  containing  chlorine  is  placed 
mouth  downwards  on  the  top  of  the  cylinder  containing 
hydrobromic  acid.  On  slipping  out  the  glass  plates  between 
the  cylinders,  the  gases  mix  and  the  brown  vapors  of  bro- 
mine are  set  free.  After  standing  for  a  few  minutes,  or, 
more  rapidly  by  shaking,  both  jars  become  filled  with  bro- 
mine vapor. 

If  a  slow  stream  of  chlorine  is  passed  through  the  recurved 
jet  (Fig.  41,  p.  S5),  and  lowered  into  a  jar  of  hydrobromic 
acid  gas,  brown  fumes  will  immediately  appear. 

Jar  of  HBr  gas  ;  jar  of  CI ;  CI  supply  ;  recurved  jet. 


^ 


L 


IODINE 

♦ 

IODINE 

PREPARATION 

1.  From  potassium  iodide,  mang^anese  dioxide  and  sul- 
phuric acid.  —  Potassium  iodide  when  acted  upon  by  sul- 
phuric acid  in  the  presence  of  an  oxidizing  agent  such  as 
manganese  dioxide  is  completely  decomposed,  the  iodine 
being  liberated. 

Three  and  one-half  grams  of  potassium  iodide  are  mixed 
with  7  g.  of  finely  pulverized  manganese  dioxide,  and  placed 
in  a  500  cc.  tubulated  retort.  One  hundred  cubic  centimeters 
of  cold  dilute  sulphuric  acid  (made  by  adding  17  cc.  of  the 
concentrated  acid  to  85  cc.  of  water)  are  added,  and  the 
mixture  thoroughly  stirred.  The  retort  is  gently  heated, 
and  vapors  of  iodine  soon  appear  and  condense  in  crystals  on 
the  neck  of  the  retort  and  in  a  flask  through  the  neck  of 
which  the  mouth  of  the  retort  is  thrust.  No  external  cool- 
ing of  the  flask  is  necessary,  and  care  should  be  taken  not 
to  heat  the  mixture  too  much. 

2  KI  -f  MnOs  -f  2  H2SO4  =  K2SO4  -f  MnS04  +  2  HgO  +  I2. 

500  cc.  tubulated  retort ;  500  cc.  flask  ;  Mn02  ;  KI ;  mixture  of  17 
cc.  cone.  H2SO4  and  85  cc.  water. 

112 


IODINE 


113 


PROPERTIES 

2.  Melting  iodine.  —  Iodine  melts  at  114°  to  a  brown 
liquid  which  solidifies  at  ordinary  temperatures  to  a  heavy 
metallic-appearing  mass. 

Three  grams  of  iodine  are  carefully  heated  in  a  clean,  dry 
test-tube,  until  completely  melted.  On  allowing  it  to  cool, 
it  solidifies,  and  by  carefully  breaking  the  test-tube  the  solid 
mass,  which  has  taken  the  form  of  the  interior  of  the  tube, 
may  be  placed  on  a  plate,  where  its  dark  color  and  metallic 
appearance  are  readily  observed. 

3.  Distillation.  —  (a)  A  few  grams  of  iodine  are  heated  in 
a  small  tubulated  retort,  the  neck  of  which  is  thrust  into 
the  mouth  of  a  large  glass  cylinder. 

On  boiling  the  iodine,  the  vapors 
partially  condense  in  the  neck  of 
the  retort,  which  should  be  as  wide 
as  possible,  and  care  should  be  taken 
that  it  does  not  become  clogged. 
The  vapor  issuing  from  the  neck 
of  the  retort  falls  by  reason  of  its 
great  weight  into  the  cylinder.  As 
the  vapors  descend  and  become 
cooled,  the  iodine  solidifies  in  min- 
ute particles,  which  fall  as  a  shower  of  glistening  crystals 
to  the  bottom  and  sides  of  the  cylinder  (Fig.  56). 

250  cc.  tubulated  retort ;  4  or  5  1.  cylinder ;  I. 

(6)  When  iodine  vapor  is  cooled  in  the  air,  the  iodine 
condenses  in  the  form  of  minute  crystals. 

Two  grams  of  iodine  are  heated  in  a  test-tube  to  boiling, 
and  the  dense  violet  vapor  poured  out  on  a  sheet  of  white 
paper.  The  iodine  settles  on  the  paper  in  the  form  of  a 
shower  of  fine  crystals. 


Fig.  56 


114  CHEMICAL   LECTURE   EXPERIMENTS 

'  4.  Volatilization  at  ordinary  temperatures.  —  Iodine  vapor- 
izes at  ordinary  temperatures,  as  may  be  seen  by  dropping 
one  or  two  small  crystals  of  iodine  into  a  3  or  4  1.  flask,  in 
the  neck  of  which  a  piece  of  paper  moistened  with  starch 
solution  is  suspended.  After  a  few  minutes  the  paper  will 
be  turned  blue  by  the  vaporized  iodine. 

3  or  4  1.  flask  ;  I  crystals  ;  starch  solution. 

5.  Solubility  in  alcohol.  —  Alcohol  dissolves  iodine  read- 
ily, with  the  formation  of  a  deep  reddish  brown  solution, 
the  so-called  tincture  of  iodine.  Two  and  a  half  grams  of 
iodine  crystals  are  placed  in  the  bottom  of  a  glass  cylinder 
and  25  cc.  of  alcohol  poured  over  them.  On  stirring  the 
mixture  with  a  rod,  the  iodine  will  be  entirely  dissolved: 

6.  Solubility  in  carbon  disulphide  and  chloroform.  —  A  few 

crystals  of  iodine  added  to  either  of  these  reagents  dissolve 
readily,  forming  a  violet  color,  in  strong  contrast  to  the 
color  iodine  gives  with  ether  or  alcohol. 

Iodine  water  is  shaken  in  a  stoppered  cylinder  with  5  cc. 
of  carbon  disulphide.  The  heavy  solvent  extracts  the  iodine 
from  the  iodine  water,  which  becomes  clear,  and  settles  to 
the  bottom  of  the  cylinder  as  a  violet-colored  liquid. 

100  cc.  stoppered  cylinder  ;  CS2  ;  CHCI3 ;  I ;  I  water. 

7.  Iodine  and  starch.  —  (a)  Iodine  forms  with  starch 
paste  a  deep  blue  color.  The  delicacy  of  this  reaction  is 
such  as  to  cause  its  use  in  many  operations  in  analytical 
chemistry. 

A  few  drops  of  starch  paste  are  added  to  a  liter  of  water. 
Iodine  water  which  contains  but  a  small  amount  of  iodine 
is  allowed  to  fall  drop  by  drop  into  the  solution.  A  very 
few  drops  will  produce  a  deep  blue  color,  thereby  showing 
the  extreme  delicacy  of  the  reaction. 


IODINE 


115 


The  color  is  discharged  by  an  excess  of  chlorine  water, 
by  heat,  and  by  alkalies. 

Starch  paste  ;  I  water. 

(b)  Effect  of  heat.  —  A  few  cubic  centimeters  of  the 
blue  liquid  are  vigorously  boiled  in  a  test-tube  for  three  or 
four  minutes.  Even  before  the  liquid  fairly  boils,  the 
color  is  completely  discharged.  On  allowing  the  test-tube 
to  stand  it  will  be  seen  that  the  color  does  not  return. 

If  the  blue  solution,  containing  a  slight  excess  of  iodine 
rather  than  of  starch,  is  heated  gently  until  the  color  is  just 
discharged,  and  then  allowed  to  cool,  the  blue  color  will 
return.  This  moderate  heating  is  best  carried  on  by 
immersing  the  test-tube  containing  the  blue  solution  in  a 
beaker  of  water  which  has  just  been  brought  to  a  boil,  and 
removed  from  the  flame.  The  color  will  shortly  disappear, 
and  if  the  tube  is  then  immediately  immersed  in  a  beaker 
of  cold  water,  the  blue  color  will  return. 

On  boiling,  the  iodine  liberated  from  the  starch  compound 
by  heat  is  volatilized  with  the  water  vapor  passing  off  into 
the  air.  If  the  blue  solu- 
tion is  heated  in  a  distill- 
ing flask,  and  the  vapor 
condensed  in  a  long  glass 
tube,  which  acts  as  an  air 
condenser  (Fig.  57),  the 
liquid  dropping  from  the 
end  of  the  tube  will  pro- 
duce a  blue  color  in  a 
beaker    of    starch    paste 

placed  beneath  it.  On  cooling,  it  will  be  found  that  the 
residue  in  the  distilling  flask  will  not  regain  its  original 
blue  color,  the  iodine  having  been  driven  off  by  boiling. 

250  cc.  distilling  flask  ;  long  glass  tube  ;  starch  solution  ;  I. 


Fig.  57 


116  CHEMICAL   LECTURE   EXPERIMENTS 

8.  Union  with  potassium.  —  On  gentle  warming,  potassium 
and  iodine  unite  with  explosive  violence. 

A  few  crystals  of  iodine  are  placed  in  a  dry  test-tube, 
and  a  3  mm.  piece  of  clean,  dry,  metallic  potassium  added. 
When  warmed,  the  elements  unite  with  a  slight  explosion, 
the  flame  possessing  the  characteristic  violet  color  of  the 
potassium  flame.  Care  should  be  taken  to  protect  the  face 
and  hands  from  the  results  of  the  reaction. 

2  K  +  I2  =  2  KI. 

Screens  ;  gauntlets  ;  K  ;  1. 

9.  Union  with  zinc  dust.  —  Zinc  dust  and  iodine  unite  in 
the  presence  of  moisture  with  the  evolution  of  heat. 

One  gram  of  zinc  dust  is  intimately  mixed  with  5  g.  of 
finely  powdered  iodine  in  a  dry  beaker.  One  or  two 
drops  of  water  are  allowed  to  fall  into  the  beaker,  when  the 
reaction  begins,  the  heat  generated  vaporizing  a  large  quan- 
tity of  iodine.  A  crystalline  sublimate  of  iodine  on  the 
walls  of  the  beaker  is  obtained. 

The  reaction  may  be  carried  out  with  a  similar  result  by 
using  iron  powder  in  the  place  of  zinc  dust. 

Zn  +  I2  =  Znlg. 

Dry  beaker  ;  Zn  dust ;  powdered  I. 

10.  Union  with  mercury.  —  Mercury  and  iodine  unite 
with  incandescence  to  form  mercuric  iodide. 

A  few  globules  of  mercury  are  heated  to  boiling  in  a  test- 
tube  clamped  in  a  vertical  position.  The  flame  is  then 
removed  and  a  few  crystals  of  iodine  dropped  into  the  hot 
mercury.  A  feeble  flame  is  observed,  and  the  iodide  of  mer- 
cury sublimes  in  a  crystalline  mass  on  the  sides  of  the  tube. 

If  both  elements  are  in  the  gaseous  form,  the  union  is 
still  more  vigorous.     The  mercury  is  heated  in  a  test-tube 


HYDRIODIC    ACID  117 

as  before,  and  the  lamp  turned  down  to  give  a  flame  just 
sufficient  to  keep  the  mercury  boiling.  A  few  crystals  of 
iodine  are  brought  to  a  boil  in  another  test-tube  and  the 
vapors  poured  upon  the  boiling  mercury.  The  union  is 
accompanied  with  a  flame,  the  product  being  deposited  as  a 
colored  crystalline  sublimate. 

Hg  +  I2  =  Hgl^. 
Dry  test-tubes  ;  Hg  ;  I. 

11.  Union  with  phosphorus.  —  Iodine  and  phosphorus 
unite,  even  in  the  cold,  with  sufficient  energy  to  ignite  the 
phosphorus. 

The  reaction  between  iodine  and  phosphorus  may  be 
readily  shown  by  placing  a  few  crystals  of  iodine  on  a  brick 
and  carefully  placing  a  small  piece  of  dried  yellow  phos- 
phorus on  top  of  the  crystals.  The  phosphorus  is  almost 
immediately  ignited. 

Brick ;  yellow  P ;  I  crystals. 


HYDRIODIC   ACID 

FORMATION  AND  PREPARATION 

12.  From  hydrogen  and  iodine.  —  Hydrogen,  mixed  with 
iodine  vapor  and  passed  through  a  heated  tube,  unites  with 
the  iodine  to  form  hydriodic  acid. 

A  few  crystals  of  iodine  are  placed  in  the  bulb  of  an  ordi- 
nary bulb-tube  with  long  arms  through  which  hydrogen 
from  a  Kipp  generator  is  passed.  A  strip  of  blue  litmus 
paper  held  in  the  issuing  gas  is  unacted  upon,  showing  the 
absence  of  acid  fumes.  The  open  arm  of  the'  bulb-tube  is 
heated  to  a  low  red  heat  by  means  of  a  Bunsen  burner,  and 
the  iodine  in  the  bulb  is  then  gently  warmed,  subliming 


118      CHEMICAL  LECTURE  EXPERIMENTS 

some  of  the  vapors  into  the  atmosphere  of  hydrogen.  The 
issuing  gas  will  now  form  white  fumes  of  hydriodic  acid 
and  a  strip  of  moistened  blue  litmus  paper  will  be  immedi- 
ately reddened.  A  piece  of  paper  moistened  with  potas- 
sium dichromate  solution  is  instantly  changed  in  color  by 
the  reducing  action  of  the  hydriodic  acid.  On  igniting  the 
gas  as  it  issues  from  the  bulb-tube,  the  heat  of  the  burning 
hydrogen  will  be  sufficient  to  decompose  the  hydriodic  acid 
with  the  liberation  of  free  iodine,  which  will  appear  as  a 
violet  vapor  rising  from  the  flame.  A  white  paper  may  be 
held  behind  the  flame  to  serve  as  a  background  for  the 
violet  vapor.  If  a  piece  of  cold  porcelain,  such  as  an  evapo- 
rating dish,  is  held  in  the  flame,  the  iodine  liberated  will 
be  deposited  as  a  brownish  yellow  mass. 

H2  -f-  I2  =  2  HI. 

Bulb-tube  ;  H  generator  ;  I ;  K2CX2O7  solution. 

13.  From  iodide  of  phosphorus  and  water.  —  Water  re- 
acts with  iodide  of  phosphorus,  liberating  hydriodic  acid 
gas. 

In  preparing  the  iodide  of  phosphorus,  2  g.  of  yel- 
low phosphorus  are  cut  in  pieces  of  approximately  .5  g. 
each,  carefully  dried  between  filter-paper  and  dropped  one 
at  a  time  on  top  of  22  g.  of  iodine  crystals  placed  in 
the  bottom  of  a  100  cc.  Jena  glass  Erlenmeyer  flask.  The 
phosphorus  should  be  dropped  as  near  the  middle  of  the 
flask  as  possible,  and  the  second  and  succeeding  pieces 
should  not  be  added  until  the  reaction  has  entirely  ceased. 
At  the  end  of  the  reaction  the  flask  will  contain  a  lique- 
fied mass  of  phosphorus  iodide. 

After  the  flask  and  its  contents  have  become  perfectly 
cold,  6  cc.  of  water  are  added,  and  a  cork  carrying  a  glass 
elbow  is  inserted  in  the  neck  of  the  flask.     A  purifying 


HYDRIODIC   ACID 


119 


U-tube  containing  red  phosphorus  should  be  connected  with 
the  glass  elbow,  the  issuing  gas  being  collected  in  dry  cylin- 
ders (Fig.  58).  The  gas  evolution  in  this  operation  is  quite 
rapid,  and  provision  should  be  made 
for  filling  several  clean,  dry  jars. 
As  the  evolution  of  gas  diminishes 
in  rapidity,  a  very  small  flame  may 
be  used  to  heat  the  contents  of  the 
flask,  which  at  the  end  of  the  oper- 
ation will  have  become  perfectly 
clear.  The  rapidity  of  the  reaction 
after   the   addition  of  water  is   so 

great  that  it  is  advisable  to  wait  a  moment  before  inserting 
the  cork  in  the  neck  of  the  flask. 


Fig.  58 


100  cc.  Jena  glass  Erlenmeyer  flask 
(yellow). 


U-tube  with  red  P;   I ;    P 


14.  By  the  action  of  iodine  on  rosin. — In  the  complex 
reaction  obtained  by  heating  a  mixture  of  iodine  and 
rosin  a  considerable  quantity  of  hydriodic  acid  gas  is 
formed. 

Fifteen  grams  of  finely  powdered  iodine  are  mixed  with 
an  equal  bulk  of  finely  powdered  rosin.  To  regulate  the 
reaction  more  satisfactorily,  the  mixture  is  intimately  rubbed 
with  an  equal  volume  of  pulverized  quartz  or  very  fine  sand. 
The  powder  is  then  placed  in  a  dry  100  cc.  Jena  glass  Erlen- 
meyer flask  fitted  with  a  one-holed  cork  and  a  glass  tube, 
7  mm.  wide,  bent  so  as  to  extend  nearly  to  the  bottom  of  a 
vertically  clamped  test-tube  (Fig.  59).  The  test-tube  is 
fitted  with  a  two-holed  stopper,  in  the  second  hole  of  which 
a  glass  elbow  is  inserted.  On  heating  the  flask,  hydriodic 
acid  gas  is  liberated,  mixed  with  considerable  quantities  of 
free  iodine  and  an  oily  liquid,  which  condenses  in  the  test- 
tube.     To  purify  the  issuing  gas  it  should  first  be  conducted 


120 


CHEMICAL  LECTURE  EXPERIMENTS 


through   a    U-tube   filled   with   red  phosphorus,  and   then 
through  a  calcium  chloride  tube.     This  method  gives  a  very 


Fig.  59 


good  yield  of  hydriodic  acid  gas  and  is  strongly  to  be  recom- 
mended. 

100  cc.  Jena  glass  Erlenmeyer  flask  ;  U-tube  filled  with  red  P  ; 
CaCl2  drying-tube  ;  powdered  quartz  or  very  fine  sand ;  powdered 
rosin  ;  I. 

15.  By  dissolving  the  gas  in  water.  —  A  very  simple 
method  of  obviating  the  difficulties  attend- 
ing the  absorption  of  this  gas  in  water  is 
that  of  conducting  the  gas  through  the 
stem  of  an  inverted  funnel,  the  mouth  of 
which  is  thrust  a  few  millimeters  under 
the  surface  of  the  w^ater  in  a  crystallizing 
dish.  If  back  suction  occurs,  air  will  be 
drawn  under  the  edge  of  the  funnel  before 
the  water  has  risen  in  the  cone  of  the 
funnel  as  far  as  the  stem. 
Fig.  60  The  funnel  may  be  replaced  by  a  retort. 


HYDRIODIC   ACID  121 


PROPERTIES 


16.  Decomposition  by  heat.  —  (a)  The  decomposition  of 
hydriodic  acid  gas  by  heat,  its  great  specific  gravity,  and 
the  fact  that  it  is  a  non-supporter  of  combustion,  are  shown 
by  pouring  500  cc.  of  the  gas  from  a  cylinder  upon  a  Bunsen 
flame  about  2  cm.  high.  Iodine  is  set  free  in  the  form  of  a 
violet  vapor  and  the  flame  is  extinguished.  As  the  hydri- 
odic acid  gas  comes  in  contact  with  the  air,  it  fumes  strongly 
from  the  absorption  of  moisture. 

500  cc.  cylinder  of  HI. 

(b)  If  a  glass  rod  is  strongly  heated  and  then  suddenly 
thrust  into  a  jar  of  the  gas,  a  combustion  is  observed  and 
iodine  vapor  is  liberated. 

17.  Acidity.  —  On  opening  a  jar  of  hydriodic  acid,  dense 
fumes  like  those  observed  about  the  mouth  of  a  concen- 
trated hydrochloric  acid  bottle,  are  formed.  If  a  piece  of 
moistened  blue  litmus  paper  is  held  over  the  mouth  of  the 
jar,  it  will  instantly  be  colored  red. 

A  rod  moistened  with  ammonium  hydroxide  gives  heavy 
white  fumes  of  ammonium  iodide  which  partially  sink  into 
the  cylinder  and  remain  suspended  in  the  heavy  gas.  A 
strip  of  paper  moistened  with  potassium  dichromate  solu- 
tion is  instantly  turned  black. 

Cylinder  of  HI  gas  ;  K2Cr207  solution. 

18.  Solubility  in  water.  —  When  a  cylinder  of  the  dry 
gas  is  opened  under  water,  the  gas  is  rapidly  absorbed,  the 
water  rising  to  take  its  place.  It  is  advisable  to  use  a 
metal  disk  to  cover  the  mouth  of  the  cylinder,  as  the  suction 
is  so  great  as  to  break  a  glass  plate. 

Metal  disk  ;  cylinder  of  HI  gas. 


122       CHEMICAL  LECTURE  EXPERIMENTS 

19.  Oxidation  by  nitric  acid.  —  The  oxidizing  action  of 
nitric  acid  on  gaseous  hydriodic  acid  is  so  great  as  to  pro- 
duce a  flame. 

Three  cubic  centimeters  of  hot  fuming  nitric  acid  are 
poured  from  a  test-tube  into  a  cylinder  of  hydriodic  acid 
gas.  A  red  flame  proceeds  from  the  cylinder  and  large 
quantities  of  violet  iodine  vapor  are  set  free. 

100  cc.  cylinder  of  HI  gas  ;  screen  ;  gauntlets  ;  fuming  HNO3. 

20.  Combustion  of  oxygen  in  hydriodic  acid  gas.  —  A 

gentle  stream  of  oxygen  is  passed  through  a  rubber  tube 
which  dips  under  water  to  determine  the  rate  of  flow  of  the 
gas.  The  rubber  tube  is  then  quickly  slipped  over  the  end 
of  a  bent  glass  tube  whose  end  has  been  heated  very  hot. 
On  suddenly  thrusting  the  tube  into  a  jar  of  hydriodic  acid 
gas,  the  oxygen  takes  fire  and  burns,  setting  free  large  quan- 
tities of  iodine. 

4  HI  -h  O2  =  2  H2O  +  2  I2. 

0  supply  ;  cylinder  of  HI  gas. 

21.  Decomposition  of  gaseous  hydriodic  acid  by  means  of 
chlorine.  —  (a)  Chlorine  reacts  with  hydriodic  acid  gas, 
forming  hydrochloric  acid  gas  and  liberating  iodine.  In  the 
presence  of  an  excess  of  chlorine,  the  liberated  iodine  com- 
bines with  the  chlorine  to  form  crystals  of  yellow  iodine 
trichloride. 

A  current  of  hydriodic  acid  gas,  prepared  as  in  Ex.  14, 
is  dried  by  being  passed  through  a  calcium  chloride  tube, 
and  is  then  conducted  through  the  recurved  jet  (Fig.  41, 
p.  85)  into  a  500  cc.  cylinder  of  chlorine.  If  the  end  of 
the  jet  has  been  warmed  a  little,  the  issuing  gas  becomes 
ignited  as  it  enters  the  chlorine,  and  burns,  liberating  iodine 
as  a  violet  vapor.      The  iodine  immediately  combines  with 


HYDRIODIC   ACID  123 

the  excess  of  chlorine,  and  the  walls  of  the  cylinder  become 
covered  with  yellow  iodine  trichloride. 

A  current  of  chlorine,  conducted  through  the  recurved  jet 
into  a  cylinder  of  hydriodic  acid  gas,  likewise  becomes 
ignited,  liberating  iodine.  As  chlorine  continues  to  be 
introduced,  the  iodine  combines  with  it,  and  is  deposited  on 
the  walls  of  the  cylinder  in  yellow  crystals  of  iodine  tri- 
chloride. 

2  HI  +  CI2  =  2  HCl  +  I2. 

I2  +  3  CI2  =  2  ICI3. 

HI  supply  ;  CaCl2  tube  ;  recurved  jet  (Fig.  41,  p.  85)  ;  500  cc. 
cylinder  of  CI ;  CI  generator  ;  500  cc.  cylinder  of  HI. 

(b)  Two  glass  cylinders  are  filled,  the  one  with  chlorine, 
the  other  with  hydriodic  acid  gas,  and  the  cylinder  contain- 
ing chlorine  is  placed  mouth  downwards  on  top  of  the 
cylinder  containing  hydriodic  acid  gas.  Glass  plates  sepa- 
rate the  two  cylinders.  On  slipping  out  the  glass  plates, 
and  allowing  the  mouths  of  the  cylinders  to  come  together, 
the  chlorine  and  hydriodic  acid  gas  interact,  iodine  being 
liberated.  A  slight  flame  is  noticed  at  first,  though  there 
is  not  enough  heat  generated  to  force  the  gases  out  into 
the  room.  As  the  hydriodic  acid  gas  is  the  heavier,  the 
progress  of  its  diffusion  into  the  lighter  chlorine  may  be 
noted  by  the  color  change  of  the  deposition  on  the  walls  of 
the  chlorine  cylinder.  At  first  in  the  upper  cylinder,  where 
there  is  an  excess  of  chlorine,  the  deposition  consists  chiefly 
of  iodine  trichloride,  a  yellow  crystalline  compound.  At 
the  end  of  the  reaction,  the  walls  of  both  cylinders  are 
covered  with  crystals  of  iodine  or  iodine  monochloride. 
This  experiment  illustrates  beautifully  the  diffusion  of 
gases. 

Cylinder  of  HI  gas  ;  cylinder  of  CI. 


124  CHEMICAL   LECTURE   EXPERIMENTS 

IODIC   ACID 

22.  Preparation  by  the  action  of  nitric  acid  on  iodine.  — 

When  iodine  is  heated  with  fuming  nitric  acid,  it  is  con- 
verted into  iodic  acid,  with  the  liberation  of  the  oxides  of 
nitrogen. 

Three  grams  of  iodine  are  placed  in  a  dry  200  cc.  Erlen- 
meyer  flask  with  40  cc.  of  fuming  nitric  acid.  The  mixture 
is  heated  for  a  few  minutes  and  the  liquid  poured  off  from 
the  undissolved  residue.  On  diluting  with  an  equal  volume 
of  water  and  shaking  with  10  cc.  of  carbon  disulphide,  the 
iodine  is  dissolved  out,  the  solution  becoming  colorless. 
The  carbon  disulphide  is  drawn  off  in  a  separating-funnel, 
and  the  upper  layer  of  liquid  tested  for  iodic  acid.  The 
liquid  is  first  filtered  to  free  from  drops  of  carbon  disulphide. 
Starch  paste  is  added  to  a  portion  of  the  solution  and  then 
a  few  drops  of  sulphur  dioxide  water.  Iodine  will  be 
liberated  and  form  the  blue  compound  with  starch.  An 
excess  of  sulphurous  acid  causes  the  decolorization  of  the 
liquid. 

3  I2  +  10  HNO3  =  6  HIO3  -f.  10  NO  4-  2  H2O. 

Separating-funnel ;  I ;  fuming  HNO3  ;  CS2  ;  SO2- water  ;  starch  paste. 

23.  Decomposition  by  heat  (iodic  anhydride).  —  Iodic  acid 
on  heating  in  a  porcelain  evaporating  dish  loses  water  and 
forms  the  anhydride,  iodic  pentoxide.  The  heating  should 
be  regular  and  should  cease  at  that  point  where  iodine 
vapors  are  liberated.  The  molten  mass  is  allowed  to  solidify 
and  is  then  used  in  the  following  experiments  on  iodic 
anhydride. 

Iodic  anhydride,  when  heated  in  a  test-tube,  gives  off 
oxygen,  with  the  liberation  of  iodine.  A  glowing  splinter 
introduced  in  the  test-tube  is  immediately  relighted. 

The  oxidizing  power  of  iodic  anhydride  may  be  shown 


IODIC   ACID  125 

by  heating  a  mixture  of  the  powdered  anhydride  and  char- 
coal powder.  The  mixture  on  heating  gives  off  violet 
vapors,  the  carbon  feebly  burning  inside  the  tube. 

A  small  quantity  of  flowers  of  sulphur  or  pulverized 
sugar  is  mixed  with  some  powdered  anhydride  and  heated 
in  a  dry  test-tube.  The  reaction  is  very  vigorous,  being 
accompanied  with  a  slight  explosion. 

2  HIO3  =  I2O5  +  H2O. 
2  lA     =  2  I2  -f  5  O2. 
HIO3 ;  I2O5 ;  powdered  charcoal  ;  S  flowers  ;  sugar. 

24.  Reduction  by  sulphurous  acid.  —  Sulphurous  acid 
acts  in  the  same  manner  as  hydriodic  acid  in  reducing 
iodic  acid.  The  reduction  is  first  accompanied  by  a  libera- 
tion of  iodine.  If,  however,  an  excess  of  sulphurous  acid  is 
added,  the  iodine  itself  becomes  converted  to  hydriodic  acid. 

If  to  a  solution  of  iodic  acid  starch  paste  is  added,  no 
color  will  appear,  as  the  combined  iodine  of  the  iodic  acid 
does  not  produce  the  blue  compound  with  starch.  On  the 
addition  of  a  few  drops  of  sulphurous  acid  the  blue  color 
will  instantly  appear.  An  excess  of  sulphurous  acid  dis- 
charges the  color. 

By  adjusting  the  concentrations  of  the  two  solutions  a 
most  interesting  experiment  on  the  time  required  for  a  re- 
action to  be  completed  may  be  made.  The  interaction  of 
sulphurous  acid  and  iodic  acid  appears  to  require  some  con- 
siderable time  to  begin,  but  having  once  started  it  proceeds 
instantaneously  throughout  the  whole  solution. 

Ten  grams  of  iodic  acid  are  dissolved  in  a  liter  of  dis- 
tilled water  and  the  solution  bottled  as  a  stock  solution  for 
use  in  this  experiment.  The  solution  is  very  permanent. 
Fifty  cubic  centimeters  of  water  are  saturated  with  sulphur 
dioxide  by  allowing  the  gas  to  bubble  through  it  for  a  few 


126  CHEMICAL   LECTURE   EXPERIMENTS 

minutes.  Twenty-five  cubic  centimeters  of  this  saturated 
sulphurous  acid  solution  are  diluted  to  a  liter  and  preserved 
in  a  bottle  as  a  stock  solution.  This  solution,  however,  as 
might  be  expected,  is  not  so  permanent  as  the  iodic  acid 
solution,  hence  it  is  advisable  to  make  it  fresh  for  every 
experiment.  Two  hundred  and  fifty  cubic  centimeters  of 
water  are  placed  in  each  of  two  clean  beakers  and  to  one 
50  cc.  of  the  stock  iodic  acid  solution,  and  to  the  other  50  cc. 
of  the  stock  sulphurous  acid  solution  are  added.  A  few 
drops  of  starch  paste  are  then  added  to  the  dilute  iodic  acid 
solution.  The  contents  of  each  beaker  are  then  stirred  to 
insure  thorough  mixing  and  then  rapidly  poured  together 
in  a  large  cylinder  capable  of  holding  700  cc.  The  mixed 
liquids  should  be  immediately  stirred  with  a  long,  clean 
stirring  rod.  No  apparent  reaction  will  take  place  for  about 
half  a  minute,  when  instantly  the  contents  of  the  whole 
cylinder  will  be  turned  a  deep  blue.  It  is  advisable  to  place 
the  cylinder  before  a  background  of  white  paper. 

The  experiment  can  be  made  still  more  striking  by  using 
a  metronome  to  indicate  the  seconds.  By  counting  off  the 
strokes  of  the  metronome  it  will  be  easy  to  state  before- 
hand on  what  stroke  the  color  change  will  occur. 

In  determining  before  the  lecture  the  length  of  time 
required  for  this  reaction,  it  is  essential  to  observe  that  no 
changes  are  made  in  the  proportions  of  the  ingredients, 
dilution,  and  temperature,  since  the  length  of  time  required 
for  the  reaction  is  greater  at  greater  dilutions  and  with  a 
higher  content  of  iodic  acid,  while  an  increase  in  tempera- 
ture shortens  the  time  required  for  the  reaction. 

2  HIO3  H-  5  SO2  -h  4  H2O  =  5  H2SO4  +  I2. 
Metronome  ;  HIO3  ;  SOa-water  (saturated)  ;  starch  paste. 


FLUORINE 


HYDROFLUORIC   ACID 

1.   Preparation  from  calcium  fluoride  and  sulphuric  acid. — 

Calcium  fluoride,  when  warmed  with  concentrated  sulphuric 
acidj  undergoes  decomposition,  with  the  formation  of  hydro- 
fluoric acid  gas  and  calcium  sulphate.  The  corrosive  action 
of  this  gas  on  glass  necessitates  that  the  operation  be  carried 
out  in  a  lead  dish  or  a  platinum  crucible. 

A  thin  paste  of  powdered  fluorspar  and  concentrated  sul- 
phuric acid  is  placed  in  a  lead  dish  or  a  platinum  crucible 
and  gently  warmed.  The  gas  is  readily  evolved  and  its 
etching  action  on  glass  is  shown  as  follows  :  — 

A  piece  of  glass  is  carefully  cleaned  and  coated  with  a 
thin  layer  of  paraffin.  By  means  of  a  sharp-pointed  pin  or 
needle  a  few  characters  are  cut  in  the  wax  coating,  care 
being  taken  to  scratch  clear  through  the  wax  down  to  the 
glass.  The  plate  is  then  placed,  with  the  waxed  surface 
down,  on  top  of  the  dish  in  which  hydrofluoric  acid  is  being 
generated  and  allowed  to  remain  there  for  from  five  to 
twenty  minutes.  Care  should  be  taken  not  to  heat  the  dish 
sufficiently  to  melt  the  wax  on  the  surface  of  the  glass  and 
thereby  spoil  the  design. 

In  case  a  platinum  crucible  is  used,  it  will  be  found  diffi- 
cult, owing  to  the  small  size  of  the  opening,  to  etch  a  design 
of  any  size.     The  gas  may  be  generated  in  the  crucible, 

127 


o 


128  CHEMICAL    LECTURE   EXPERIMENTS 

however,  and  retained  in  a  paper  box  of  sufficient  size  to 
expose  a  much  larger  surface  of  glass  to  the  action  of  the 
gas.     A  round  pill  box,  some  8  to  10  cm.  in  diameter,  has  a 

hole  cut  in  the  bottom  a  littte 
smaller  than  the  maximum  di- 
ameter of  the  platinum  crucible 
(Fig.  61).  The  crucible  is  then 
crowded  down  into  the  hole  un- 
til its  rim  is  but  a  few  millime- 

FiG.  61 

ters  above  the  bottom  of  the  box. 
The  paste  of  calcium  fluoride  and  concentrated  sulphuric 
acid  is  very  gently  warmed  in  the  platinum  crucible,  the 
gaseous  fumes  ascending  into  the  pill  box.  A  large  glass 
plate  may  be  prepared  and  etched  as  described  above. 

CaF2  +  H2SO4  =  CaS04  4-  2  HF. 

Lead  dish  or  platinum  crucible  ;  large  pill  box  ;  waxed  glass  plates  ; 
CaFa. 

2.  Acidity.  —  The  gas  formed  in  the  preceding  experi- 
ment will  immediately  redden  a  piece  of  moistened  blue 
litmus  paper. 

3.  Etching  glass  with  aqueous  hydrofluoric  acid. — Aque- 
ous hydrofluoric  acid  is  obtainable  in  the  market  in  rubber 
or  paraffin  bottles,  and  is  much  used  in  analytical  operations. 
This  aqueous  solution  etches  glass  fully  as  well  as  the  gas. 

A  glass  plate  is  coated  with  wax,  prepared  as  described  in 
Ex.  1,  and  a  piece  of  filter-paper  moistened  with  the  aqueous 
hydrofluoric  acid  laid  on  top  of  the  wax.  In  a  few  minutes 
the  etching  will  be  complete. 

If  a  small  rim  of  wax  of  sufficient  height  is  made  around 
the  design,  the  aqueous  acid  may  be  poured  directly  upon  the 
wax,  and  being  retained  by  the  rim  will  effect  the  etching  as 
before. 


FLUORINE 


129 


In  either  of  these  experiments  a  paste  of  calcium  fluoride 
and  concentrated  sulphuric  acid  may  be  substituted  for  the 
aqueous  hydrofluoric  acid. 

Waxed  glass  plate  ;  aqueous  HF  ;  CaF2  (powdered). 

4.    Corrosive  action  of  hydrofluoric  acid  on  glass.  —  The 

corrosive  action  of  aqueous  hydrofluoric 
acid  on  glass  and  the  consequent  necessity 
of  using  bottles  other  than  glass  for  hold- 
ing this  liquid  may  be  shown  by  placing 
50  cc.  of  the  solution  in  a  thin  200  cc. 
Erlenmeyer  flask  and  gently  warming. 
The  flask  should  be  set  in  an  iron  or, 
better,  a  platinum  evaporating  dish  which 
is  kept  warm  by  a  water-bath  (Fig.  62). 
A  rubber  stopper  fitted  with  a  short  glass 
elbow  and  a  rubber  tube  conducts  the 
fumes  into  the  flue.  In  a  short  time 
(from  one-half  to  three-quarters  of  an 
hour)  the  acid  will  have  eaten  through 
the  bottom  of  the  flask  and  run  into  the  platinum  evapo- 
rating dish. 

Thin  flask  ;  iron  or  platinum  dish  ;  aqueous  HF. 


Fig.  62 


<s^ 


iA^- 


C? 


^K 


SULPHUR 


SULPHUR 


PROPERTIES 

1.  Roll  sulphur.  —  Sulphur  is  a  very  poor  conductor  of 
both  heat  and  electricity  and,  when  gently  warmed,  at  times 
even  by  the  warmth  of  the  hand,  the  roll  will  break  in  pieces. 

A  roll  of  sulphur  is  laid  on  a  piece  of  asbestos  paper  and 
very  gently  warmed  with  a  low  flame.  It  will  crackle  and 
fall  in  pieces,  owing  to  the  unequal  expansion  produced  by 
the  heat. 

Asbestos  paper  ;  roll  of  S. 

2.  Distillation  of  sulphur  and  preparation  of  sulphur 
flowers.  —  The  vapors  of  sulphur,  when  allowed  to  escape 

into  the  air,  condense  in  the 
form  of  a  fine  dust,  the  so-called 
flowers  of  sulphur. 

A  retort  is  one-third  filled 
with  roll  sulphur,  and  the  neck 
of  the  retort,  which  should  be 
as  short  as  possible,  thrust  in 
the  mouth  of  a  bottle,  which  is 
laid  on  its  side  and  has  a  layer 
of  asbestos  paper,  10  cm.  wide, 
along  its  length  (Fig.  63).  The 
sulphur  is  brought  to  a  boil  by  means  of  a  powerful  burner 
and  large  quantities  of  the  vapor  are  driven  into  the  bot- 

130 


Fig.  G3 


SULPHUR  131 

tie.  An  asbestos  covering  should  be  made  fot^the  mouth 
of  the  bottle  and  provided  with  a  hole  througft  ^v^oh  the  . 
neck  of  the  retort  may  be  thrust.  A  considerable' poflbion? 
of  the  sulphur  vapor  will  condense  in  the  ^eck  of '  th^etorl^*- 
and  drop  as  a  liquid  upon  the  asbestos  pafter?  T^'  vapja^S" 
will  fill  the  bottle  and  be  deposited  all  ovier  th^sides  ^S'a 
fine  powder.  "   ■  ••'* 

200  cc.  retort ;  asbestos  paper  ;  bottle  ;  large  burner  ;  roll  S. 

3.  Preparation  of  plastic  sulphur.  —  (a)  Sulphur,  when 
heated  above  its  melting  point,  is  changed  into  a  black  vis- 
cous mass  having  the  properties  of  rubber. 

K-oll  sulphur  is  gently  heated  in  a  100  cc.  Erlenmeyer 
flask  and  very  carefully  melted.  A  clear,  yellow  liquid 
results.  If  some  of  this  light  yellow  liquid  is  poured  into 
water,  it  will  solidify  to  a  hard,  light  yellow,  opaque  mass. 
On  heating  still  further,  however,  the  liquid  becomes  viscous 
and  turns  black,  and  the  sulphur  will  not  flow  out,  even  if 
the  flask  is  held  mouth  downwards. 

If  the  liquid  is  heated  still  further,  it  again  becomes  more 
fluid,  and  can  then  be  poured  into  cold  water  in  a  beaker.  A 
funnel  is  placed  mouth  downwards  in  the  beaker,  and  the  thin 
stream  of  melted  sulphur  is  poured  around  the  stem  of  the 
funnel,  forming  a  coil  of  solidified  sulphur  in  the  beaker 
(Fig.  64).  On  removing  the  sulphur  from  the  beaker  it  will 
be  found  to  be  elastic  and  plastic. 

(b)  A  200  cc.  glass-stoppered  tubulated  retort,  preferably 
with  a  wide  neck,  is  one-third  filled  with  lumps  of  sulphur 
and  clamped  in  such  a  position  that  it  may  be  strongly 
heated  in  a  large  Bunsen  burner.  A  sheet  of  asbestos  paper 
is  laid  over  the  top  of  the  retort,  extending  almost  to  the 
mouth,  and  held  in  place  by  having  the  stopper  of  the  retort 
thrust  through  it.  The  contents  of  the  retort  a?e  then 
melted  and  the  heat  gradually  increased  until  they  are  vig- 


132 


CHEMICAL   LECTURE   EXPERIMENTS 


orously  boiling.  The  vapor  partially  condenses  in  the  neck 
of  the  retort  and  falls  in  a  thin  stream  into  a  large  beaker 
of  water,  in  which  is  immersed  an  inverted  funnel  about  the 
diameter  of  the  beaker  (Fig.  64).  The  sulphur  solidifies,  and 
the  beaker  should  be  slowly  revolved 
to  allow  the  sulphur  to  collect  in  a 
spiral  form  on  the  funnel.  It  is  ad- 
visable to  ignite  the  sulphur  vapor  not 
condensed  in  the  neck  of  the  retort,  as 
otherwise  the  flowers  of  sulphur  will 
settle  on  the  surface  of  the  water  and 
interfere  with  the  proper  cooling  of 
the  sulphur.  When  the  contents  of 
the  retort  are  vigorously  boiling,  a 
flame  of  sulphur  vapor,  some  10  to  15  cm.  in  length,  issues 
from  the  mouth  of  the  retort.  It  is  best  to  stop  the  heat 
before  all  the  sulphur  has  been  distilled.  On  withdraw- 
ing the  funnel  from  the  beaker  the  sulphur  will  be  found 
as  a  bundle  of  fine  threads  and  will  possess  elastic 
qualities. 

200  cc.  retort ;  large  burner ;  beaker  and  funnel ;  S. 


Fig.  64 


4.   Crystallization  from  fusion   (prismatic  sulphur). — A 

150  cc.  Jena  glass  beaker  is  two-thirds  filled  with  roll  sul- 
phur, which  is  then  carefully  melted,  care  being  taken  to 
keep  the  temperature  as  low  as  possible.  When  the  sulphur 
is  completely  melted,  the  flame  is  removed  and  the  beaker 
imbedded  in  a  dish  of  sand.  As  soon  as  it  is  cooled  suf- 
ficiently to  form  a  crust  on  the  surface,  a  hole  is  made 
through  the  crust  and  the  remaining  melted  sulphur  poured 
out  into  water.  A  fine  network  of  yellowish,  transparent 
crystals  will  have  formed  all  around  the  walls  of  the 
beakei^  the  needles  extending  into  the  centre  of  the 
mass. 


SULPHUR  133 

5.  Crystallization  from  carbon  disulphide  (octahedral  sul- 
phur).—  Sulphur  is  quite  soluble  in  carbon  disulphide,  and 
crystallizes  from  its  solution  in  this  solvent  in  octahedrons. 

Twenty  grams  of  pulverized  roll  sulphur  are  placed  in  a 
100  cc.  flask  and  covered  with  50  cc.  of  carbon  disulphide. 
The  flask  is  then  tightly  closed  with  a  cork  (a  rubber  stop- 
per cannot  be  used)  and  vigorously  shaken.  After  a  few 
moments  the  solution  is  allowed  to  stand,  and  the  clear 
supernatant  liquid  decanted  into  a  glass  evaporating  dish. 
As  the  liquid  evaporates,  the  sulphur  is  deposited  in  octa- 
hedral crystals. 

Glass  evaporating  dish  ;  roll  S  ;  CS2. 

6.  Union  with  iron  powder.  —  Iron  powder,  when  heated 
with  twice  its  volume  of  sulphur  flowers,  combines  with  the 
latter  with  the  evolution  of  heat  and  light  to  form  ferrous 
sulphide.  The  mixture  is  gently  heated  in  a  hard-glass 
test-tube  throughout  the  whole  mass,  and  then  the  temper- 
ature is  materially  increased  at  the  bottom.  The  union  of 
the  elements  begins  at  this  point  and  proceeds  with  a  great 
evolution  of  heat  and  light  through  the  contents  of  the  test- 
tube. 

A  modification  may  be  introduced  by  placing  a  small  heap 
of  the  mixture  of  iron  powder  and  sulphur  flowers  on  a  plate 
and  touching  it  at  one  point  with  a  hot  glass  rod.  The 
mixture  ignites,  and  the  whole  mass  is  soon  converted  to 
ferrous  sulphide. 

Fe  -f  S  =  FeS. 

"Fe  powder ;  S  flowers. 

7.  Union  with  iron  at  ordinary  temperatures.  —  Iron  pow- 
der and  sulphur  flowers  unite  at  ordinary  temperatures  when 
mixed  with  a  small  quantity  of  water. 

Twenty-two  grams  of  iron  powder  and  15  g.  of  sulphur 


134  CHEMICAL  LECTURE   EXPERIMENTS 

flowers  are  rubbed  together  in  a  mortar  with  7  cc.  of  water. 
After  a  thorough  mixing  the  damp  powder  is  placed  on  a 
white  plate  and  moulded  into  a  conical  heap.  The  mixture 
is  pressed  firmly  down  with  the  fingers  and  allowed  to  stand 
some  15  to  20  minutes.  Soon  the  mixture  heats,  and  the 
cone  cracks  open  and  steam  is  seen  to  rise.  The  whole  mass 
becomes  black  in  color.  That  iron  sulphide  is  actually 
formed  is  easily  shown  by  adding  some  hydrochloric  acid  to 
a  small  quantity  of  the  black  powder  and  testing  the  hydro- 
gen sulphide  evolved. 
Fe  powder  ;  S  flowers. 

8.  Combustion  of  iron  in  sulphur  vapor.  —  Red-hot  iron, 
when  thrust  into  sulphur  vapor,  combines  with  the  sulphur 
with  incandescence,  forming  ferrous  sulphide. 

Sulphur  is  brought  to  a  boil  in  a  hard-glass  test-tube  and 
a  piece  of  common  iron  wire  gauze  heated  to  redness  in  a 
Bunsen  burner.  On  thrusting  the  gauze  into  the  boiling 
sulphur  the  union  takes  place,  the  molten  iron  sulphide  fall- 
ing to  the  bottom  of  the  test-tube. 

9.  Union  with  copper.  —  (a)  Sulphur  in  a  100  cc.  Jena 
glass  flask  is  heated  to  boiling  and  the  sulphur  vapor  allowed 
to  burn  at  the  mouth.  A  spiral  of  copper  made  by  winding 
fine  copper  wire  around  a  rod,  or  a  piece  of  fine  copper  gauze 
is  thrust  into  the  neck  of  the  flask  through  the  flame  of 
burning  sulphur.  The  two  elements  unite  with  an  evolu- 
tion of  light  and  heat. 

Cu  -f-  S  =  CuS. 

Fine  copper  wire  or  fine  copper  gauze  ;  roll  S. 

(6)  A  space,  1  cm.  square,  in  a  piece  of  thin  sheet  copper 
is  heated  strongly.  When  very  hot  a  small  bit  of  sulphur  is 
thrown  upon  it.  The  sulphur  and  copper  unite,  forming 
cupric  sulphide,  which  remains  as  a  bi*ight  metallic  black 


HYDROGEN   SULPHIDE  135 

spot  in  the  centre  of  the  sheet.     The  brittle  nature  of  the 
product  is  shown  by  thrusting  the  point  of  a  lead  pencil 
through  the  spot. 
Cu  sheet ;  S. 

10.  Combustion  of  magnesium  in  sulphur  vapor.  —  Burning 
magnesium,  when  lowered  into  sulphur  vapor,  continues  to 
burn  with  the  formation  of  magnesium  sulphide. 

Sulphur  is  brought  to  a  boil  in  a  100  cc.  flask  and  a  15  cm. 
strip  of  magnesium  ribbon  is  ignited  in  the  air.  When  the 
magnesium  is  burning  freely,  it  is  lowered  through  the  mouth 
of  the  flask  into  the  sulphur  vapor,  where  it  continues  to 
burn  with  the  formation  of  magnesium  sulphide. 

Mg  +  S  =  MgS. 
Boiling  S  ;  Mg  ribbon. 

11.  Combustion  of  zinc  and  sulphur.  —  A  mixture  of  two 
parts  of  zinc  and  one  part  of  sulphur  flowers,  when  thrown 
into  a  hot  iron  dish  or  saucer,  burns  violently,  forming  zinc 
sulphide. 

This  mixture  is  also  readily  ignited  by  touching  it  with  a 
hot  glass  rod.  A  small  heap  of  the  mixed  powders  is  placed 
on  a  brick  or  a  piece  of  asbestos  paper  and  touched  with  a 
glass  rod  which  has  been  heated  in  the  Bunsen  flame. 

Zn  +  S  =  ZnS. 
Iron  dish  or  crucible  ;  Zn  dust ;  S  flowers. 

HYDROGEN    SULPHIDE 

PREPARATION 

12.  By  the  union  of  hydrogen  and  sulphur.  — Hydrogen, 
when  passed  over  sulphur  in  the  cold,  has  no  action  on  the 
element,  though,  if  the  sulphur  is  heated,  a  portion  of  it 
combines  with  the  hydrogen  to  form  hydrogen  sulphide. 


136       CHEMICAL  LECTURE  EXPEKIMENTS 

A  small  lump  of  sulphur  is  placed  in  a  bulb-tube  through 
which  dry  hydrogen  is  conducted.  An  elbow  attached  to 
the  end  of  the  bulb-tube  dips  into  lead  acetate  solution.  No 
change  is  observed  in  the  lead  acetate  solution  until  the  sul- 
phur is  heated,  when,  almost  immediately,  the  presence  of 
hydrogen  sulphide  is  shown  in  the  issuing  gas  by  the  forma- 
tion of  a  black  precipitate  of  lead  sulphide  in  the  solution. 

Instead  of  using  the  bulb-tube,  the  sulphur  may  be  placed 
in  a  dry  test-tube,  fitted  with  a  two-holed  cork.  Hydrogen 
is  conducted  through  a  glass  elbow  in  the  cork  extending 
to  the  bottom  of  the  test-tube,  and  issues  through  a  glass 
elbow  in  the  other  hole  of  the  cork.  A  paper  moistened 
with  lead  acetate  solution  held  in  the  issuing  gas  remains 
unchanged  until  the  sulphur  is  warmed,  when  it  is  imme- 
diately blackened  by  the  hydrogen  sulphide  formed. 

I12  -f-  S  =  H2S. 
Bulb-tube  ;  H  generator ;  S. 

13.  From  the  reduction  of  sulphur  dioxide  by  means  of 
hydrogen  in  the  presence  of  platinized  asbestos.  —  Sulphur 
dioxide,  when  mixed  with  hydrogen  and  passed  over  heated 
platinized  asbestos,  is  reduced  to  sulphur,  which  is  depos- 
ited in  the  tube.  The  excess  of  hydrogen  reacting  on  the 
heated  sulphur  produces  a  small  amount  of  hydrogen  sul- 
phide, which  may  be  tested  in  the  issuing  gas. 

The  apparatus  (Fig.  69,  p.  159)  is  adapted  for  this  pur- 
pose, hydrogen  being  substituted  for  the  oxygen.  The  hy- 
drogen and  sulphur  dioxide  bubbling  through  the  sulphuric 
acid  mix  and  pass  out  through  the  third  neck  into  the 
bulb-tube  containing  platinized  asbestos.  Uiitil  the  plati- 
num is  heated  no  reaction  takes  place,  but  on  warming 
the  bulb  the  platinized  asbestos  will  be  seen  to  glow,  and 
a  deposit  of  sulphur  will  appear  in  the  farther  end  of  the 


HYDROGEN    SULPHIDE  137 

tube.  The  issuing  gas,  when  tested  with  a  piece  of  paper 
moistened  with  lead  acetate  solution,  shows  the  presence  of 
hydrogen  sulphide. 

3-necked  Wolff  bottle  ;   H  generator ;   SO2  generator  ;    platinized 

asbestos. 

14.  From  ferrous  sulphide  and  hydrochloric  or  sulphuric 
acid.  —  Ferrous  sulphide,  when  treated  with  dilute  sulphuric 
acid,  or,  better,  hydrochloric  acid,  liberates  large  quantities 
of  hydrogen  sulphide.  Though  the  gas  generated  by  this 
operation  is  not  perfectly  pure,  containing,  as  it  does,  con- 
siderable quantities  of  hydrogen,  it  is  used,  nevertheless, 
for  almost  all  analytical  operations,  as  it  is  an  indispensable 
adjunct  in  analytical  chemistry.  Unfortunately  the  evil- 
smelling  and  poisonous  properties  of  the  gas  necessitate 
special  precautions  in  its  preparation,  collection,  and  use. 

The  gas  is  readily  prepared  by  placing  a  few  lumps  of 
ferrous  sulphide  in  the  gas  generator  (Ex.  7,  p.  43).  Dilute 
sulphuric  acid  (1  volume  of  concentrated  acid  to  14  of 
water),  or,  better,  dilute  hydrochloric  acid  (1  volume  of  con- 
centrated acid  to  1  of  water),  is  poured  through  the  thistle- 
tube.  The  reaction  begins  almost  immediately.  The  gas 
should  be  dried  by  means  of  calcium  chloride  only,  as  it  is 
decomposed  by  sulphuric  acid. 

In  case  but  a  small  quantity  of  the  gas  is  desired,  the 
apparatus  as  above  described  is  satisfactory,  though  it  is 
necessary  to  prevent  any  quantity  of  the  gas  from  escaping 
into  the  room.  This  can  best  be  accomplished  by  inserting 
after  the  wash-bottle  a  three-way  stop-cock,  such  as  is  shown 
in  Fig.  39,  p.  81.  One  arm  of  the  stop-cock  is  connected 
with  the  flue  or  with  some  suitable  absorbing  bottle,  the 
other  directly  with  the  apparatus  into  which  the  hydrogen 
sulphide  is  to  be  conducted. 

Innumerable  devices  for  the  evolution  of  hydrogen  sul- 


138  CHEMICAL  LECTURE  EXPERIMENTS 

phide  have  been  described  in  chemical  journals,  but  as  yet 
no  ideal  portable  apparatus  for  supplying  a  constant  stream 
of  this  gas  has  been  devised.  The  simplest  form  is  proba- 
bly the  Kipp  generator,  the  middle  bulb  being  filled  with 
lumps  of  ferrous  sulphide  as  large  as  can  conveniently  pass 
through  the  tubulature,  while  the  acid  chamber  is  filled  with 
sulphuric  or  hydrochloric  acid  diluted  as  described  above. 
The  replenishment  of  this  apparatus  with  acid  and  ferrous 
sulphide  is,  however,  a  very  disagreeable  task,  and  conse- 
quently a  great  drawback  to  its  general  use. 

In  most  laboratories  large  quantities  of  hydrogen  sulphide 
are  prepared  for  use  with  classes  in  qualitative  and  quanti- 
tative analysis.  The  ideal  arrangement  is  that  in  which 
distilled  water  is  supercharged  with  the  gas  and  retained  in 
tin-lined  steel  cylinders.  This  method  is  the  one  adopted 
in  the  chemical  laboratory  of  Harvard  College.  The  num- 
ber of  forms  of  apparatus  for  preparing  the  gas  on  the 
small  scale  is  only  exceeded  by  the  number  of  devices  for 
preparing  it  on  a  large  scale  for  classes  of  students.  While 
each  has  its  merits,  a  description  is  given  in  the  Appendix 
(p.  420),  of  the  apparatus  used  in  Wesleyan  University, 
which  for  regularity,  simplicity,  and  economy  is  not  excelled 
by  any  other  form  known  to  the  writer. 

For  lecture-table  purposes  the  arrangement  for  obtaining 
hydrogen  sulphide  is  to  conduct  a  separate  pipe  (preferably 
a  quarter-inch  lead  pipe)  from  the  large  generator  to  a  glass 
stop-cock  securely  fastened  to  a  partition  under  the  lecture 
table.  A  second  tube  is  then  connected  with  the  glass  stop- 
cock, which  conducts  the  gas  to  a  metal  cock  on  the  top  of 
the  table,  where  by  simply  turning  the  cock  a  full  supply  of 
the  gas  is  instantly  secured.  The  glass  stop-cock  is  used  to 
cut  off  the  gas  when  not  in  use,  and  is  preferable  to  a  metal 
cock  on  account  of  its  non-corrosive  character,  'during  the 
lecture  the  metal  stop-cock  on  the  upper  part  of  the  desk 


HYDROGEN   SULPHIDE  139 

may  be  used  for  regulating  the  supply  of  gas,  though  the 
supply  should  be  cut  off  with  the  glass  stop-cock  at  the  end 
of  the  lecture.  This  arrangement  can  be  applied  to  many 
of  the  existing  forms  of  hydrogen  sulphide  generators,  and 
is  by  far  the  most  satisfactory  method  of  obtaining  this  gas 
for  lecture  table  purposes. 

FeS  -h  2  HCl  =  FeCl2  +  H2S. 

FeS  +  H2SO4  =  FeS04  +  HgS. 

Gas  generator  (Ex.  7,  p.  81)  ;  three-way  cock  ;  FeS. 

15.  By  the  action  of  hydrochloric  acid  on  antimony  sul- 
phide. — Native  antimonious  sulphide  (stibnite)  yields,  when 
treated  with  hydrochloric  acid,  a  very  pure  form  of  hydrogen 
sulphide  uncontaminated  with  free  hydrogen. 

A  few  grams  of  the  pulverized  mineral  are  placed  in  a 
300  cc.  Erlenmeyer  flask  fitted  with  a  dropping-funnel  and 
elbow  (Fig.  3,  p.  11).  Concentrated  hydrochloric  acid  is 
allowed  to  drop  into  the  flask,  which  is  gently  warmed.  A 
steady  evolution  of  pure  hydrogen  sulphide  is  obtained. 

A  measured  volume  of  this  gas  will  be  almost  completely 
absorbed  by  sodium  hydroxide,  as  shown  in  Ex.  18. 

Sb^Sg  +  6  HCl  =  2  SbClg  +  3  US- 

300  cc. -Erlenmeyer  flask  ;  dropping-funnel  ;  eudiometer  (Fig.  11, 
p.  26)  ;  stibnite. 

PROPERTIES 

16.  Collection  of  the  gas.  —  (a)  In  many  experiments  it  is 
necessary  to  use  dry  hydrogen  sulphide  in  dry  containers. 
As  this  gas  is  somewhat  heavier  than  air,  it  can  be  collected 
by  displacement,  though  provision  should  be  made  to  conduct 
.the  excess  of  the  gas  into  the  flue  or  some  proper  absorber. 

A  cylinder  is  fitted  with  a  two-holed  rubber  stopper.  A 
glass  tube  extends  to  the  bottom  of  the  cylinder  through  one 


140  CHEMICAL   LECTURE   EXPERIMENTS 

of  the  holes  in  the  cork,  and  through  the  other  hole  a  glass 
elbow  is  thrust.  The  hydrogen  sulphide  is  conducted  through 
the  long  tube  to  the  bottom  of  the  jar,  where  it  collects  and 
forces  the  air  out  through  the  elbow  at  the  top.  When  the 
jar  is  full,  the  cork  is  rapidly  withdrawn  and  a  glass  plate 
slipped  over  the  mouth  of  the  jar.  The  cork  should  be 
immediately  thrust  into  a  second  cylinder. 

The  acid  nature  of  the  gas,  as  well  as  its  aqueous  solution, 
should  be  shown. 

(b)  Owing  to  its  solubility  in  cold  water,  it  is  essential 
when  collecting  this  gas  over  water,  to  have  the  water  as 
warm  as  possible,  and  to  use  only  a  porcelain  or  glass  dish 
as  a  pneumatic  trough.  The  gas  is  much  less  soluble  in  salt 
solution  than  in  water,  and  may  accordingly  be  collected  over 
brine. 

Porcelain  or  glass  pneumatic  trough  ;  H2S  generator  ;  hot  water  ; 
sat.  sol.  NaCl. 

17.  Solubility  in  water.  —  (a)  Hydrogen  sulphide  is  read- 
ily absorbed  by  water. 

A  eudiometer  tube  is  two-thirds  filled  with  hydrogen  sul- 
phide, the  thumb  placed  over  the  mouth  of  the  tube  and  the 
tube  shaken  thoroughly.  The  gas  will  dissolve  in  the  water 
remaining  in  the  tube,  producing  a  suction,  and  if  the  tube 
is  opened  under  water,  the  water  will  rise  inside,  ^he  cur- 
rent of  hydrogen  sulphide  used  to  fill  the  tube  should  be 
very  rapid,  so  as  to  prevent  the  water  from  being  saturated 
with  the  gas  while  the  tube  is  being  filled. 

(b)  The  eudiometer  (Fig.  11,  p.  26)  may  be  used  in  this 
experiment,  in  which  case  it  is  filled  with  hydrogen  sulphide 
over  water  and  ice-cold  water  allowed  to  flow  down  the 
inside  of  the  tube  into  the  gas.  As  the  gas  is  absorbed,  the 
level  of  the  water  in  the  tube  rises. 

HgS  generator  ;   eudiometer  (Fig.  11,  p.  26)  ;  ice- water. 


HYDROGEN    SULPHIDE  141 

(c)  A  flask  is  rapidly  filled  with  hydrogen  sulphide  over 
water  until  half  of  the  water  in  the  flask  has  been  driven 
out.  The  palm  of  the  hand  is  then  placed  on  the  mouth  of 
the  flask,  which  is  thoroughly  shaken.  The  gas  is  absorbed 
by  the  water,  producing  a  suction  capable  of  supporting  the 
flask  in  a  hanging  position  in  the  palm  of  the  hand. 

In  case  the  water  in  the  flask  becomes  saturated  with  the 
gas,  which  is  almost  sure  to  happen  if  the  current  is  not 
rapid,  the  operation  is  best  performed  by  filling  the  flask 
completely  with  the  gas  and  then  pouring  in  one-third  of  its 
volume  of  ice-cold  water.  On  covering  the  flask  with  the 
moistened  palm  and  shaking  it,  a  very  strong  suction  will  be 
obtained. 

Stout- walled  flask  ;  H2S  generator  ;  ice-water. 

(d)  A  saturated  solution  of  the  gas  may  be  obtained  by 
using  the  apparatus.  Fig.  85,  p.  196. 

18.  Solubility  in  sodium  hydroxide.  —  The  solubility  of 
hydrogen  sulphide  in  sodium  hydroxide  is  shown  by  filling 
the  eudiometer  (Fig.  11,  p.  26)  with  hydrogen  sulphide  over 
a  saturated  solution  of  sodium  chloride.  Sodium  hydroxide 
is  allowed  to  flow  through  the  stop-cock  into  the  gas,  which 
will  immediately  be  absorbed  and  the  liquid  will  rise  inside 
the  tube. 

If  the  hydrogen  sulphide  is  prepared  from  commercial 
ferrous  sulphide,  considerable  hydrogen  gas  will  be  present 
in  the  evolved  gas  and  therefore  be  unabsorbed  by  the  sodium 
hydroxide. 

If  the  hydrogen  sulphide  is  prepared  from  the  action  of 
hydrochloric  acid  on  antimony  sulphide,  the  gas  will  be 
much  more  pure,  and  but  a  small  quantity  of  gas  will  remain 
unabsorbed,  i.e.,  less  than  half  a  cubic  centimeter  out  of 
TOO  cc.  of  hydrogen  sulphide. 


142  CHEMICAL  LECTURE  EXPERIMENTS 

19.  Combustion  in  air.  —  Hydrogen  sulphide,  though  a 
non-supporter  of  combustion,  burns  with  a  blue  flame. 

A  lighted  candle  lowered  into  a  jar  containing  hydrogen 
sulphide  is  extinguished,  and  the  hydrogen  sulphide  ignited. 
The  gas  burns  at  the  mouth  of  the  jar,  but  owing  to  the 
deficiency  of  oxygen  in  the  lower  portions  of  the  jar,  the 
sulphur  is  deposited  instead  of  being  oxidized  as  fast  as  it  is 
liberated,  hence  the  walls  of  the  jar  become  covered  with  a 
thin  film  of  flowers  of  sulphur. 

To  demonstrate  especially  this  latter  phenomenon,  it  is 
advisable  to  have  a  tall  jar,  as  this  form  retards  the  entrance 
of  the  air. 

Tall  jar  of  H2S  ;  candle  on  wire. 

20.  Deposition  of  sulphur  in  the  incomplete  combustion  of 
hydrogen  sulphide.  —  If  air  is  burned  in  an  atmosphere  of 
hydrogen  sulphide,  the  heat  from  the  flame  will  be  sufficient 
to  cause  a  decomposition  of  the  surrounding  gas  with  an 
accompanying  deposition  of  sulphur. 

The  apparatus  with  which  this  flame  of  air  is  produced,  is 
that  shown  in  Fig.  142,  p.  341.  A  strong  current  of  hydro- 
gen sulphide  is  conducted  through  the  elbow  in  the  bottom 
of  the  lamp  chimney  and  is  ignited  at  the  orifice  at  the  top. 
A  gentle  current  of  air,  best  obtained  from  the  water  blast, 
is  passed  through  the  long  tube,  which  may  be  pushed  up 
through  the  hole  in  the  cork  into  the  centre  of  the  hydrogen 
sulphide  flame  at  the  top  of  the  lamp  chimney.  On  slowly 
lowering  the  tube,  the  air  will  be  seen  to  be  burning  in  the 
atmosphere  of  hydrogen  sulphide,  and  a  deposit  of  sulphur 
will  be  obtained  on  the  walls  of  the  chimney. 

Lamp  chimney  and  fittings  (Fig.  142,  p.  341)  ;  H2S  generator ;  air- 
blast  or  gasometer. 

21.  Becomposition  in  a  hot  tube.  —  Dry  hydrogen  sulphide, 
when  passed  through  a  glass  tube  which  is  strongly  heated 


HYDROGEN   SULPHIDE 


143 


with   a  Bunsen  burner,  is  decomposed,  and  sulphur  is  de- 
posited on  the  cooler  portions  of  the  tube. 

22.  Explosion  of  a  mixture  of  hydrogen  sulphide  and 
oxygen.  —  A  round-bottomed  ginger-ale  bottle  is  filled  with 
three  volumes  of  oxygen  and  two  volumes  of  hydrogen 
sulphide.  The  mixture  is  well  shaken,  and  then  a  flame 
held  at  the  mouth  of  the  bottle. 

2  H2S  -f-  3  O2  =  2  H2O  +  2  SO2. 

23.  Action  on  sulphur  dioxide.  —  (a)  In  the  presence  of  a 
small  amount  of  moisture,  hydrogen  sulphide  reacts  with 
sulphur  dioxide,  with  the  liberation  of  sulphur.  This  re- 
action is  of  especial  interest  in  indicating  the  deposition  of 
sulphur  in  volcanoes.  The  operation  may  be  carried  out  in 
the  simplest  manner  by  inverting  a  cylinder  of  hydrogen 
sulphide  collected  over  water,  mouth  downwards,  on  top  of  a 
cylinder  of  equal  size,  containing  sulphur  dioxide.  When 
the  glass  plates  are  slipped  from  between  the  two  cylinders, 
the  gases  unite  with  a  heavy  deposition  of  sulphur  on  the 
walls  of  the  cylinders.  As  the  sul- 
phur dioxide  is  nearly  twice  as  heavy 
as  the  hydrogen  sulphide,  the  diffu- 
sion of  the  two  gases  is  somewhat 
slow,  and  gives  an  excellent  illustra- 
tion of  this  phenomenon.  In  case 
it  is  desired  to  hasten  the  action,  the 
cylinders  are  shaken. 

The  reaction  may  be  shown  on  a 
much  more  extended   scale  by  con- 
ducting the  two  gases  from  suitable 
generators  into  a  large  three-necked  Wolff  bottle  (Fig.  65). 
Hydrogen  sulphide  is  conducted  through  one  neck  of  the 


Fig.  65 


144  CHEMICAL   LECTURE   EXPERIMENTS 

Wolff  bottle,  and  sulphur  dioxide  through  another.  The 
third  neck  is  fitted  with  a  cork,  carrying  a  glass  elbow  con- 
nected with  the  flue.  After  a  few  minutes,  the  whole 
interior  of  the  Wolff  bottle  becomes  coated  with  a  layer 
of  finely  divided  sulphur. 

The  bottle  should  be  cleaned  immediately  after  use,  as 
the  sulphur,  if  allowed  to  dry  on  the  walls  of  the  bottle,  is 
very  hard  to  remove.  The  reaction  is  not  altogether  as 
simple  as  is  given  in  Equation  (1)  below,  as  a  certain  small 
quantity  of  pentathionic  acid  is  formed. 

(1)  SO2  +  2  HoS  =  2  H2O  +  3  S. 

(2)  5  SO2  +  5  HgS  =  H2S5O6  +  4  H2O  +  5  S. 

Wolff  bottle  (3-necked)  ;  H2S  generator ;  SO2  generator  ;  cylinder 
of  H2S  ;  cylinder  of  SO2. 

(6)  The  interaction  of  hydrogen  sulphide  and  sulphur 
dioxide  may  also  be  carried  out  in  aqueous  solution.  Aque- 
ous solutions  of  the  two  gases,  when  mixed,  produce  a  heavy 
precipitate  of  sulphur. 

By  conducting  hydrogen  sulphide  into  a  solution  of  sul- 
phur dioxide,  or  by  conducting  sulphur  dioxide  into  a  solu- 
tion of  hydrogen  sulphide,  the  precipitate  of  sulphur  is  also 
obtained. 

24.  Combustion  of  iron.  —  A  bundle  of  iron  wires,  or 
better,  a  bit  of  steel  wool  (Ex.  16,  p.  23),  when  held  in  the 
flame  of  burning  hydrogen  sulphide,  will  take  fire  in  the 
gas  and  burn,  forming  ferrous  sulphide. 

H2S  supply  ;  steel  wool. 

25.  Ignition  by  fuming  nitric  acid.  —  Strong  oxidizing 
agents,  such  as  fuming  nitric  acid,  elfect  the  rapid  oxida- 
tion and  subsequent  ignition  of  hydrogen  sulphide. 

A  300   CO.   cylinder   is   filled   with   hydrogen   sulphide, 


HYDROGEN   SULPHIDE  145 

covered  with  a  ground-glass  plate,  and  placed  mouth  up- 
wards on  the  table.  A  few  cubic  centimeters  of  fuming 
nitric  acid  are  gently  warmed  and  poured  into  the  jar  of  the 
gas.  The  hydrogen  sulphide  is  ignited,  with  a  slight  ex- 
plosion, and  care  should  be  taken  to  avoid  danger  from  the 
spurting  out  of  drops  of  acid.  Dense  fumes  of  nitrogen 
oxides  are  evolved,  and  sulphur  is  deposited  on  the  walls  of 
the  cylinder. 

300  cc.  cylinder  of  H2S ;  fuming  HNOg. 

26.  Decomposition  by  sodium.  —  Hydrogen  sulphide,  when 
passed  over  heated  sodium,  is  decomposed,  the  sulphur 
uniting  with  the  sodium  to  form  sodium  sulphide,  and  the 
hydrogen  escaping  from  the  tube. 

A  few  small  pieces  of  sodium,  which  should  be  dried  and 
freed  from  crust,  are  placed  in  a  hard-glass  bulb-tube 
through  which  a  current  of  hydrogen  sulphide  is  being 
passed.  On  heating  the  metal  gently  it  takes  fire,  glowing 
brightly,  and  the  issuing  hydrogen,  when  ignited,  burns  with 
a  yellow  sodium  flame.  The  yellow  residue  in  the  bulb  con- 
sists of  sodium  sulphide,  which  may  be  dissolved  out  with 
water  and  tested. 

H2S  -I-  2  Na  =  NagS  +  Hg. 

Bulb-tube  ;  H2S  supply  ;  Na. 

27.  Action  on  solutions  of  metallic  salts.  —  The  great 
importance  of  the  use  of  hydrogen  sulphide  in  analytical 
chemistry  renders  a  study  of  its  action  on  solutions  of  me- 
tallic salts  essential.  The  simplest  method  of  showing  its 
action  is  by  adding  small  portions  of  an  aqueous  solution 
of  hydrogen  sulphide  to  solutions,  of  the  various  metals  in 
small  cylinders.  The  following  selection  of  metals  shows 
the  great  variety  of  color  in  the  sulphides  and  the  necessity 
of  an  alkaline  solution  to  effect  the  precipitation  of  the  sul- 


146  CHEMICAL   LECTURE   EXPERIMENTS 

phide  from  certain  salt  solutions.  The  cylinders  should 
contain  respectively  solutions  of  cupric  sulphate,  antimoni- 
ous  chloride,  cadmium  chloride,  lead  nitrate,  zinc  sulphate, 
manganese  sulphate,  and  cobalt  nitrate.  In  preparing  the 
solution  of  antimonious  chloride  the  addition  of  tartaric 
acid  will  prevent  the  precipitation  of  the  white  oxychloride. 
The  solutions  of  zinc,  manganese,  and  cobalt  give  no  precipi- 
tate with  hydrogen  sulphide,  though  on  the  addition  of  a 
small  quantity  of  ammonium  hydroxide  the  sulphides  are 
immediately  precipitated. 

The  operation  may  also  be  carried  out  by  passing  hydro- 
gen sulphide  through  the  various  salt  solutions  contained 
in  gas  washing-bottles.  The  hydrogen  sulphide  generator 
used  in  this  experiment  must  have  a  very  long  safety-tube 
to  permit  an  increase  of  pressure  within  the  generator 
sufficient  to  cause  the  gas  to  bubble  through  the  successive 
liquids.  To  hasten  the  operation,  dilute  solutions  of  the 
salts  are  used.  The  cylinders  are  connected  in  series  in 
the  order  above  indicated.  In  case  a  Kipp  generator  is 
used  to  furnish  the  hydrogen  sulphide,  the  necessary  press- 
ure is  obtained  by  inserting  a  cork  carrying  a  short  glass 
tube,  a  rubber  tube,  and  a  pinch-cock  into  the  opening  in 
the  top  of  the  generator.  By  closing  the  pinch-cock  when 
the  generator  is  in  operation  the  acid  is  prevented  from 
rising  into  the  acid  reservoir,  and  consequently  a  greater 
pressure  is  obtained.  The  rubber  tube  and  pinch-cock  may 
be  replaced  by  a  safety-funnel  containing  mercury. 

CUSO4  +  H2S  =  CuS  -f  H2SO4. 

2  SbClg  +  3  HgS  =  SbgSg  +  6  HCl. 

etc.  etc. 

Seven  gas  washing-bottles  ;  H2S  generator,  with  extra  long  thistle 
or  Kipp  H2S  generator  ;  solutions  of  CUSO4,  SbCls,  C(iCl2,  Pb(N03)2, 
ZnS04,  MnS04,  Co(N03)2. 


HYDROGEN   PERSULPHIDE  147 

HYDROGEN   PERSULPHIDE 

28.  Preparation  by  the  action  of  hydrochloric  acid  on 
calcium  polysulphide.  —  Calcium  polysulphide  is  made  by 
adding  40  g.  of  sulphur  flowers  to  300  cc.  of  water,  to  which 
20  g.  of  quicklime  have  been  added.  The  mixture  is  boiled 
ten  minutes,  and  then  allowed  to  settle.  The  cooled  liquid 
is  decanted  off  and  poured  in  a  thin  stream  into  a  mixture 
of  100  cc.  of  hydrochloric  acid  and  50  cc.  of  water,  in  a 
liter  separating-funnel,  which  is  shaken  during  the  addition. 
After  a  few  minutes  the  greater  portion  of  the  hydrogen 
persulphide  formed  will  have  settled  to  the  bottom  of  the 
funnel  as  a  heavy,  yellowish  oil.  The  oil  is  drawn  off  into 
a  small  flask  containing  fused  calcium  chloride,  where  it 
is  dried. 

CaSs  +  2  HCl  =  H2S2  +  CaCla  +  3  S.     [?] 
Liter  separating-funnel ;  small  flask  ;  CaO  ;  S  flowers  ;  fused  CaCl2. 

29.  Solubility  in  carbon  disulphide.  —  Hydrogen  persul- 
phide is  mixed  in  a  test-tube  with  two  or  three  times  its 
volume  of  carbon  disulphide.  The  two  liquids  are  perfectly 
miscible,  and  the  solution  remains  undecomposed  much 
longer  than  the  pure  hydrogen  persulphide. 

H2S2  ;  CS2. 

30.  Bleaching  action.  —  Very  dilute  litmus  solution,  when 
added  to  two  drops  of  hydrogen  persulphide  in  a  test-tube, 
is  bleached.  The  reaction  is  not  immediate,  and  follows 
only  after  vigorous  shaking.     Sulphur  is  precipitated. 

31.  Decomposition  in  an  alkaline  solution.  —  Hydrogen 
sulphide,  like  hydrogen  peroxide,  is  more  stable  in  an  acid 
than  in  an  alkaline  solution.  The  compound  decomposes  in 
a  dilute  alkaline  solution,  setting  free  sulphur  and  forming 
hydrogen  sulphide. 


148 


CHEMICAL  LECTURE  EXPERIMENTS 


Fifty  cubic  centimeters  of  water  are  added  to  2  drops  of 
hydrogen  persulphide  in  a  100  cc.  flask.  One  drop  of  sodium 
hydroxide  solution  is  added,  and  the  mixture  vigorously 
shaken.  Almost  immediately,  even  in  the  cold,  the  liquid 
becomes  turbid  from  sulphur  precipitated,  and  on  warming 
the  solution,  hydrogen  sulphide  is  expelled. 

H2S2  =  HgS  4"  S. 

32.  Reduction  of  silver  oxide.  —  Hydrogen  persulphide, 
like  hydrogen  peroxide,  reduces  silver  oxide.  A  few  centi- 
grams of  silver  oxide  are  allowed  to  fall  upon  2  drops  of 
hydrogen  persulphide  in  a  dry  test-tube.  The  reaction  is 
vigorous. 

SULPHUR   MONOCHLORIDE 

33.  Preparation  by  the  action  of  chlorine  on  sulphur.  — 

Dry  chlorine  acts  on  sulphur  with  the  production  of  a  yel- 
low, oily  liquid,  sulphur  monochloride. 

A  400  cc.  tubulated  retort  is  one-third  filled  with  flowers 
of  sulphur.    Dry  chlorine  is  conducted  through  a  glass  elbow 

inserted  in  the  tubulature, 
and  the  neck  of  the  retort 
is  thrust  into  a  filter  bottle, 
whose  side  tube  is  connected 
with  a  draft  (Fig.  66).  Pro- 
vision should  be  made  for 
heating  the  sulphur  and 
cooling  the  receiver.  The 
sulphur  is  strongly  heated, 
and  the  chlorine  current 
Pjq  gg  maintained  at  a  rapid  rate. 

The  tube  conducting  the 
chlorine  should  be  lowered  so  as  to  almost  touch  the  sur- 
face of  the  melted  sulphur.     After  a  few  cubic  centimeters 


SULPHUR   DIOXIDE  149 

of  the  chloride  have  collected  in  the  receiver  the  operation 
should  be  stopped. 

2  S  +  CI2  =  S2CI2. 

400  cc.  tubulated  retort ;  filter-flask  ;  S  flowers  ;  CI  generator. 

34.  Solubility  of  sulphur  in  sulphur  monochloride. — A 

few  pieces  of  sulphur  are  placed  in  a  test-tube  and  cov- 
ered with  sulphur  monochloride.  By  shaking,  or  more 
rapidly  by  gentle  boiling,  the  sulphur  is  completely 
dissolved. 

35.  Decomposition  by  water.  —  Sulphur  monochloride, 
when  allowed  to  stand  in  contact  with  water,  is  gradually 
decomposed  with  the  liberation  of  sulphur  and  hydrogen 
sulphide.  One  cubic  centimeter  of  sulphur  monochloride  is 
placed  in  a  test-tube  with  2  or  3  cc.  of  water  and  vigorously 
shaken.  The  decomposition  is  rapid  and  the  contents  of 
the  tube  become  warm. 

SULPHUR  DIOXIDE  AND  SULPHUROUS  ACID 

PREPARATION 

36.  From  sulphur  and  oxygen.  —  Sulphur  burns  in  the 
air  or  in  pure  oxygen  to  form  sulphur  dioxide. 

A  40  cm.  length  of  combustion-tube,  provided  with  a 
cork  at  each  end,  is  clamped  in  a  horizontal  position,  and  a 

wad  of  asbestos  or  glass  wool  ,_,., _^ 

placed  at  one  end  of  the  tube.  ^^' 

A  boat,  in  which  a  few  pieces  * 
of  roll  sulphur  are  placed,  is 
inserted  in  the  other  end  of  the  tube,  and  a  gentle  stream 
of  oxygen  is  admitted,  driving  out  all  air.  The  cork  is 
withdrawn,  the  sulphur  ignited,  and  the  current  of  oxygen 
continued  through  the  tube.  The  sulphur  burns  with  a  blue 
flame,  forming  sulphur  •  dioxide,  which  escapes  at  the  other 


150 


CHEMICAL  LECTURE  EXPERIMENTS 


end  of  the  combustion-tube.  The  plug  of  asbestos  serves 
to  retain  any  unburned  sulphur  which  may  distil  over. 
The  issuing  gas  may  be  collected  in  cylinders  by  displace- 
ment and  used  in  any  of  the  experiments  described  beyond. 

40   cm.    length  combustion-tube  (Fig.  67)  ;   porcelain  boat ;  glass 
wool  or  fibrous  asbestos  ;  S  ;  O  supply. 


37.  Volumetric  relation  of  the  sulphur  dioxide  formed  to 
the  oxygen  used.  —  Sulphur,  when  burned  in  an  atmosphere 
of  oxygen,  yields  one  volume  of  sulphur  dioxide  for  each 
volume  of  oxygen  consumed,  hence  in  burning  sulphur  in 
a  confined  volume  of  oxygen  the  volume  of  the  product 
remains  the  same  as  the  volume  of  the  oxygen  used. 

A  700  cc.  Jena  glass  distillation  flask  is  filled  with  dry 
oxygen  by  displacement,  and  the  arm  connected  with  one 
limb  of  a  U-tube  half  filled  with  mercury  (Fig.  68).     The 

cork  is  provided  with  a  glass  rod 
carrying  a  small  platinum  defla- 
grating-spoon  at  the  end,  in  which 
sulphur  is  burned.  The  deflagra^ 
ting-spoon  is  easily  made  from 
a  small  piece  of  platinum  foil 
which  is  fastened  to  the  glass 
rod  by  means  of  platinum  wire. 
A  4  mm.  piece  of  roll  sulphur  is 
placed  in  the  platinum  spoon,  and 
after  ignition  in  the  air,  is  im- 
mediately thrust  into  the  flask, 
where  it  continues  to  burn  with 
great  brilliancy.  The  cork  must  be  firmly  inserted  in  the 
neck  of  the  flask,  and  the  union  between  the  U-tube  and  the 
flask  must  be  very  tight.  As  the  sulphur  burns,  the  gases 
expand,  and  the  mercury  rises  in  the  open  arm  of  the  U- 
tube.     On  cooling,  the  gases  contract,  and  at  the  end  of  the 


Fig.  68 


SULPHUR   DIOXIDE  151 

operation  the  level  in  the  arms  of  the  U-tube  will  be  found 
to  be  the  same. 

700  cc.  Jena  glass  distillation  flask ;  1-holed  rubber  stopper ; 
U-tube  ;  platinum  deflagrating-spoon  ;  Hg  ;  S. 

38.  From  sulphuric  acid  and  copper.  —  Sulphuric  acid, 
when  heated  with  copper,  becomes  reduced,  liberating  sul- 
phur dioxide.  This  reaction  was  formerly  used  to  prepare 
the  gas  on  the  lecture  table,  but  the  method  of  Experiment 
41  is  preferable. 

The  gas  may  be  prepared  on  the  small  scale  by  heating  a 
few  grams  of  copper  clippings  with  concentrated  sulphuric 
acid  in  a  100  cc.  Erlenmeyer  Jena  glass  flask. 

Cu  +  2  H2SO4  =  CuSO,  -f-  2  H2O  -f  SO2. 
100  cc.  Erlenmeyer  flask  ;  Cu  clippings. 

39.  From  sulphuric  acid  and  powdered  charcoaL  —  Char- 
coal reduces  sulphuric  acid,  with  the  formation  of  varying 
amounts  of  sulphur  dioxide,  carbon  monoxide  and  dioxide. 

The  impure  gas  may  be  made  by  heating  a  thin  paste  of 
powdered  charcoal  and  concentrated  sulphuric  acid  in  a  100 
cc.  Jena  glass  Erlenmeyer  flask.  The  reaction  requires  con- 
siderable heat  to  start,  but  after  a  short  time  sulphur 
dioxide  may  be  detected  at  the  mouth  of  the  flask. 

4  H2SO4  -f-  3  C  =  4  H2O  +  4  SO2  +  CO2  +  2  CO. 
100  cc.  Jena  glass  Erlenmeyer  flask  ;  powdered  charcoal. 

40.  From  sulphuric  acid  and  sulphur.  —  Sulphur  reacts 
with  hot  concentrated  sulphuric  acid  to  form  sulphur 
dioxide. 

A  thin  paste  of  sulphur  flowers  and  concentrated  sul- 
phuric acid  is  heated  in  a  100  cc.  Jena  glass  Erlenmeyer 
flask.  As  the  temperature  of  the  sulphuric  acid  rises 
almost  to  the   boiling   point,   the   reaction    begins.      The 


152  CHEMICAL   LECTURE   EXPERIMENTS 

sulphur  melts  to  a  globule,  and  thus  presents  but  little  sur- 
face for  the  action  of  the  acid,  hence  the  quantity  of 
sulphur  dioxide  formed  is  very  small. 

2  H2SO4  +  S  =  2  H2O  +  3  SO2. 
100  cc.  Jena  glass  Erlenmeyer  flask;  S  flowers. 

41.  By  the  action  of  sulphuric  acid  on  sodium  acid  sul- 
phite.—  By  far  the  most  satisfactory  method  for  the  prepa- 
ration of  sulphur  dioxide  is  that  in  which  the  reaction 
between  sulphuric  acid  and  sodium  acid  sulphite  is  used. 
This  latter  compound  can  be  readily  obtained  in  the  mar- 
ket at  a  very  low  price. 

Sodium  acid  sulphite  is  placed  in  the  bottom  of  the  300 
cc.  Erlenmeyer  flask  of  the  apparatus  (Fig.  45,  p.  92).  The 
dropping-funnel  is  filled  with  dilute  sulphuric  acid,  made 
by  pouring  one  volume  of  concentrated  sulphuric  acid  into 
an  equal  volume  of  water  and  cooling  the  mixture.  The 
glass  elbow  is  connected  with  a  gas  washing-bottle  contain- 
ing concentrated  sulphuric  acid,  and  the  dry  gas  is  col- 
lected by  displacement  in  two  or  three  empty  cylinders. 
On  allowing  the  dilute  sulphuric  acid  to  drop  slowly  upon 
the  sodium  acid  sulphite,  a  very  regular  evolution  of  sul- 
phur dioxide  is  obtained. 

2  NaHSOg  -f-  H2SO4  =  Na2S04  -f-  2  SO2  +  2  H2O. 

300  cc.  Erlenmeyer  flask  ;  dropping-funnel ;  NaHSOg  ;  dil.  H2SO4 
(1:1). 

PROPERTIES 

42.  Liquefaction  of  sulphur  dioxide.  —  Pure  dry  sulphur 
dioxide,  when  passed  through  a  tube  immersed  in  a  freez- 
ing mixture,  condenses  to  a  colorless  liquid. 

Sulphur  dioxide  generated  according  to  the  method  of 
the  preceding  experiment  is  first  dried  by  passing  through 
a  gas  washing-bottle   containing  sulphuric  acid,  and  then 


SULPHUR    DIOXIDE  153 

conducted  into  a  U-tube  immersed  in  salt  and  ice.  The  gas 
is  there  liquefied.  Many  expensive  tubes  in  which  to  con- 
dense the  gas  are  on  the  market,  though,  unless  large 
quantities  of  the  liquid  sulphur  dioxide  are  required,  the 
operation  is  well  shown  by  the  ordinary  U-tube. 

The  liquefied  gas  is  readily  obtained  in  small  tin  cylin- 
ders at  a  low  price,  and  is  best  used  in  this  form  for  the 
experiments  on  the  production  of  cold  by  its  evaporation. 
The  cans  are  cooled  in  a  mixture  of  salt  and  ice  before 
being  opened,  and  if  they  are  kept  immersed  in  the  freez- 
ing mixture,  there  will  be  no  great  loss  by  evaporation. 

U-tube ;  ice  and  salt ;  SO2  generator. 

43.  Freezing    action    of    liquefied    sulphur    dioxide. — 

(a)  Liquid  sulphur  dioxide,  when  allowed  to  evaporate 
spontaneously,  produces  an  intense  cold  which  may  be 
utilized  to  freeze  water. 

Five  cubic  centimeters  of  liquid  sulphur  dioxide  are 
poured  on  10  cc.  of  water  in  a  small  beaker.  The  mixture 
is  stirred  and  immediately  solidifies  to  a  crystalline  mass. 
Provision  should  be  made  for  the  escape,  into  the  flue  or 
hood,  of  the  vapors  of  sulphur  dioxide. 

(b)  A  few  drops  of  water  are  placed  on  a  block  of  wood 
and  a  small  beaker  set  on  the  wet  portion.  On  pouring  5  cc. 
of  liquefied  sulphur  dioxide  into  the  beaker,  the  liquefied 
gas  evaporates,  producing  an  intense  cold.  The  water 
under  the  beaker  freezing  causes  the  wood  to  adhere  to  the 
beaker. 

Block  of  wood  ;  liquefied  SO2. 

44.  Production  of  the  Leidenfrost  phenomenon  with  lique- 
fied sulphur  dioxide.  —  Liquefied  sulphur  dioxide,  when 
thrown  into  a  hot  platinum  dish,  assumes  the  spheroidal 
state,    giving   a   striking   illustration    of    the   Leidenfrost 


154  CHEMICAL   LECTURE   EXPERIMENTS 

phenomenon  of  a  liquid,  which  boils  below  zero,  remaining 
in  the  liquid  form  in  a  red-hot  dish. 

A  platinum  dish  is  brought  to  a  red  heat  in  a  powerful 
Bunsen  lamp  and  10  cc.  of  liquefied  sulphur  dioxide  poured 
into  it.  Instantly  the  liquid  assumes  the  spheroidal  form, 
and  may  be  poured  out  of  the  dish  upon  a  plate. 

The  experiment  may  be  made  still  more  striking  by  fol- 
lowing the  introduction  of  the  liquid  sulphur  dioxide  by  an 
immediate  addition  of  10  cc.  of  water  to  the  contents  of  the 
platinum  dish.  If  the  dish  is  then  quickly  removed  by 
means  of  crucible  tongs  and  the  contents  thrown  on  a  plate, 
it  will  be  seen  that  sufficient  sulphur  dioxide  has  remained 
unvolatilized  to  freeze  the  water,  which  will  remain  in  the 
plate  in  the  form  of  ice. 

Platinum  dish  ;  plate  ;    liquefied  SO2. 

45.  Specific  gravity  of  gaseous  sulphur  dioxide.  —  Sul- 
phur dioxide  is  twice  as  heavy  as  air,  and  when  a  liter 
of  the  gas  is  poured  into  a  beaker  on  a  balance  arm,  as 
in  Ex.  9,  p.  47,  a  marked  deflection  of  the  pointer  is 
obtained. 

If  a  liter  of  the  gas  is  poured  upon  the  paper  wheel  de- 
scribed in  Ex.  36,  p.  313,  it  may  be  made  to  rotate. 

Lecture-balance  ;  paper  wheel  (Fig.  126,  p.  313)  ;  liter  cylinder  of 
SO2. 

46.  Action  on  litmus.  —  A  moistened  strip  of  blue  litmus 
paper  is  thrust  into  a  jar  of  the  gas,  where,  owing  to  the 
acid  nature  of  the  sulphur  dioxide,  it  is  instantly  turned 
red. 

47.  Action  on  potassium  dichromate  solution.  —  Five  cubic 
centimeters  of  potassium  dichromate  solution,  when  poured 
into  the  gas,  are  immediately  turned  green,  owing  to  the 
reducing  action  of  the  sulphur  dioxide. 


SULPHUROUS   ACID  165 

48.  Solubility  in  water.  —  (a)  If  a  small  piece  of  ice  or 
a  few  drops  of  water  are  allowed  to  enter  a  tube  of  the  gas 
collected  over  mercury,  the  absorption  is  very  rapid,  the 
mercury  rising  to  take  the  place  of  the  absorbed  gas. 

(b)  A  cylinder  filled  with  sulphur  dioxide  is  opened 
mouth  downwards  under  water.  The  gas  is  absorbed  and 
the  water  rises  and  completely  fills  the  cylinder. 

SO2  in  tube  collected  over  mercury;  ice. 

49.  The  gas  does  not  support  the  combustion  of  a  candle. 

—  A  lighted  candle  or  a  burning  taper,  when  lowered  into 
the  gas,  is  immediately  extinguished. 

50.  Bleaching  action. —  Sulphur  dioxide  is  a  powerful 
bleaching  agent  and  is  much  used  for  this  purpose  in  techni- 
cal chemistry.  Its  bleaching  action  is  best  shown  by  de- 
colorizing a  red  rose  with  the  gas.  The  rose  is  lowered  into 
a  jar  of  sulphur  dioxide  and  allowed  to  remain  there  some 
minutes.  The  color  will  rapidly  disappear.  The  color  may 
be  restored  by  holding  the  flower  in  chlorine  or  in  the  vapor 
of  fuming  nitric  acid.  The  restoration  of  the  color  depends 
upon  the  fact  that  the  sulphur  dioxide  is  oxidized  to  sul- 
phuric acid  by  chlorine  and  fuming  nitric  acid. 

SO2  gas  ;  jar  of  CI ;  fuming  HNO3 ;  red  rose. 

51.  Restoration  of  the  color  to  a  rose  bleached  by  sulphur 
dioxide.  —  The  colorless  compound  formed  by  the  union  of 
sulphur  dioxide  with  the  coloring  matter  of  the  flower  is 
destroyed  by  the  action  of  sulphuric  acid,  hence  by  immers- 
ing the  rose  bleached  in  the  preceding  experiment  in  50 
per  cent  sulphuric  acid  the  color  is  restored.  The  acid 
should  be  prepared  and  cooled  before  use. 

Rose  from  preceding  experiment ;  H2SO4  (50  per  cent). 


156  CHEMICAL   LECTURE   EXPERIMENTS 

52.  Combustion  of  iron  or  tin.  —  Sulphur  dioxide,  while 
not  supporting  the  combustion  of  carbonaceous  material, 
will  support  the  combustion  of  certain  of  the  metals. 

A  small  quantity  of  iron  or  tin  powder  is  placed  in  a 
bulb-tube  through  which  a  gentle  stream  of  sulphur  dioxide 
is  conducted.  On  heating  the  iron  powder  it  glows,  with 
the  formation  of  iron  sulphide  and  oxide. 

Bulb-tube  ;  SO2  generator  ;  Fe  powder  ;  powdered  Sn. 

53.  Union  of  sulphur  dioxide  and  lead  dioxide.  —  Sulphur 
dioxide  and  lead  dioxide  unite  directly  to  form  lead  sul- 
phate. 

A  small  quantity  of  well-dried  lead  dioxide  is  placed  on 
a  piece  of  asbestos  paper  covering  the  bowl  of  a  deflagrat- 
ing-spoon.  On  lowering  the  spoon  into  a  jar  of  dry  sulphur 
dioxide  the  dark-colored  oxide  is  converted  to  white  lead 
sulphate,  the  change  being  accompanied  by  a  strong  glowing. 

The  union  may  also  be  accomplished  by  conducting  a 
stream  of  sulphur  dioxide  through  a  bulb-tube  containing  a 
quantity  of  the  lead  dioxide. 

Pb02  +  SO2  =  PbS04. 

Bulb-tube  ;  deflagrating-spoon  ;  asbestos  paper  ;  SO2  supply  ;  jar  of 
SO2 ;  PbOa. 

54.  Reduction  of  potassium  permanganate  solution.  —  The 

intense  color  of  the  solution  of  potassium  permanganate  is 
immediately  discharged  by  adding  sulphur  dioxide  water  to 
it  in  a  cylinder. 

The  experiment  can  be  varied  by  allowing  the  deep-col- 
ored permanganate  solution  to  flow  from  a  burette  into  a 
cylinder  of  the  sulphur  dioxide  solution.  As  the  perman- 
ganate drops  into  the  sulphurous  acid  its  color  vanishes 
until  all  the  sulphurous  acid  has  been  oxidized,  when  one 


HYDROSULPHUROUS    ACID  157 

more  drop  of  the  permanganate  will  permanently  color  the 
whole  solution.  The  permanganate  solution  should  in  each 
case  be  acidified  with  sulphuric  acid  to  prevent  the  precipi- 
tation of  oxides  of  manganese. 

Burette  ;  KMn04  solution  ;  SO2  water. 

55.  Electrolysis  of  sulphurous  acid.  —  Nascent  oxygen  and 
hydrogen  react  with  sulphurous  acid,  forming  in  the  first 
case  sulphuric  acid,  and  in  the  second  reducing  the  sulphu- 
rous acid  to  sulphur. 

A  10  per  cent  solution  of  sulphuric  acid  is  saturated  with 
sulphur  dioxide  and  the  liquid  placed  in  the  electrolytic 
apparatus  (Fig.  46,  p.  95).  On  passing  a  current  from  a 
bichromate  battery  through  the  platinum  electrodes,  it  will 
be  found  that  very  little,  if  any,  gas  collects  in  the  tubes. 
The  oxygen  liberated  at  the  positive  pole  is  used  up  in  oxi- 
dizing the  sulphurous  acid  to  sulphuric  acid,  while  the 
hydrogen  formed  at  the  negative  pole  immediately  effects 
the  reduction  of  the  sulphurous  acid  to  sulphur.  The  liquid 
around  the  negative  pole  becomes  milky  from  the  liberation 
of  free  sulphur. 

Electrolytic  apparatus  (Fig.  46,  p.  95)  ;  Pt  electrodes ;  bichromate 
battery  ;   10  per  cent  H2SO4  saturated  with  SO2. 

HYDROSULPHUROUS   ACID 

56.  Preparation.  —  Sulphur  dioxide  water  or  sulphurous 
acid  in  the  presence  of  finely  divided  zinc  is  reduced  to 
hydro-  or  hyposulphurous  acid. 

A  100  cc.  Erlenmeyer  flask  is  half  filled  with  a  saturated 
solution  of  sulphur  dioxide  in  water  and  a  few  grams  of  pul- 
verized zinc  are  added.  The  solution,  which  contains  free 
hydrosulphurous  acid,  becomes  somewhat  yellowish,  and  a 
portion  of  the  zinc  is  dissolved.     As  the  reaction  continues, 


158  CHEMICAL    LECTURE   EXPERIMENTS 

the  acid  is  decomposed  and  a  small  quantity  of  sulphur  is 
precipitated. 

H2S03+H2=H2S02  +  HA 

SO2  water  ;  granulated  Zn. 

57.  Bleaching  action.  —  Indigo  solution,  which  is  not 
bleached  by  sulphurous  acid,  is  readily  bleached  by  hydro- 
sulphurous  acid.  A  small  quantity  of  indigo  solution  is 
placed  in  each  of  two  cylinders.  Sulphurous  acid  is  added 
to  the  first,  and  hydrosulphurous  acid  to  the  second.  The 
latter  only  is  bleached.    Litmus  paper  is  similarly  bleached. 

H2SO2 ;  indigo  solution. 

58.  Reducing  action.  —  Hydrosulphurous  acid  possesses 
strong  reducing  properties  and  precipitates  the  metals  mer- 
cury and  silver  from  solutions  of  their  soluble  salts.  The 
reactions  may  be  carried  out  in  test-tubes  by  adding  a  small 
quantity  of  hydrosulphurous  acid  to  the  respective  salt 
solutions. 

The  reaction  with  cupric  sulphate  proceeds  in  two  stages. 
A  small  quantity  of  the  hydrosulphurous  acid  is  added  to 
the  dilute  cupric  sulphate  solution,  which  is  rapidly  turned 
from  blue  to  green.  As  the  reaction  proceeds,  the  solution 
changes  to  a  dark  brown,  and  a  precipitate  is  obtained  con- 
sisting of  metallic  copper  and  cuprous  hydride. 

The  addition  of  sulphurous  acid  to  cupric  sulphate  solu- 
tion produces  no  precipitate. 

Solutions  of  H2SO2,  H2SO3,  HgClg,  AgNOg,  CuSO^. 

SULPHUR  TRIOXIDE 

PREPARATION 

59.  By  the  union  of  oxygen  and  sulphur  dioxide  in  the 
presence  of  platinized  asbestos.  —  (a)    When  a  mixture  of 


Fia. 


SULPHUR   TRIOXIDE  169 

sulphur  dioxide  and  oxygen  is  passed  over  heated  platin- 
ized asbestos,  sulphur  trioxide  is  formed. 

A  500  cc.  3-necked  Wolff  bottle  is  half  filled  with  concen- 
trated sulphuric  acid.  A  current  of  sulphur  dioxide  is  con- 
ducted through  a  glass  tube  inserted  in  one  of  the  necks  of 
the  Wolff  bottle  and  dipping  beneath  the  surface  of  the 
sulphuric  acid.  A  glass  tube,  conducting  oxygen,  is  thrust 
through  another  neck  of 
the  bottle  and  likewise 
dips  beneath  the  surface 
of  the  acid.  A  short  glass 
elbow  is  inserted  in  the 
cork  in  the  third  neck 
and  is  connected  with  a 
bulb-tube  or  combustion- 
tube  containing  a  3  or  4  cm.  length  of  platinized  asbestos 
(Fig.  69).  The  gases  are  passed  with  approximately  the 
same  degree  of  rapidity  into  the  bottle  and  proceed  un- 
changed through  the  platinized  asbestos  and  bulb-tube  into 
the  air.  On  heating  the  platinized  asbestos,  however,  dense 
white  clouds  of  sulphur  trioxide  are  formed. 

2  SO2  -f  O2  =  2  SO3. 

500  cc.  3-necked  Wolff  bottle  (Fig.  69) ;  bulb-tube ;  SO2  generator  ; 
O  supply  ;  Pt  asbestos. 

(b)  Instead  of  passing  a  mixture  of  gaseous  oxygen  and 
sulphur  dioxide  over  platinized  asbestos,  the  simpler  process 
of  passing  oxygen  first  through  strong  sulphur  dioxide  water, 
and  then  through  concentrated  sulphuric  acid,  and  finally 
over  platinized  asbestos,  may  be  used. 

A  current  of  oxygen  is  passed  through  a  saturated  solu- 
tion of  sulphur  dioxide  in  water  in  a  200  cc.  Erlenmeyer 
flask,  which  is  gently  warmed.  The  oxygen  there  mixes 
with  the  sulphur  dioxide,  and  the  two  gases  are  conducted 


160  CHEMICAL   LECTURE   EXPERIMENTS 

through  a  gas  washing-bottle  containing  concentrated  sul- 
phuric acid.  The  mixed  gases  are  then  conducted  through 
a  bulb-tube  or  combustion-tube  containing  platinized  asbes- 
tos. On  heating  the  platinized  asbestos  dense  clouds  of  sul- 
phur trioxide  issue  from  the  tube. 

200  cc.  Erlenmeyer  flask  ;  bulb  with  platinized  asbestos  ;  H2SO4  gas 
washing-bottle  ;  O  supply  ;  saturated  solution  of  SO2. 

60.  From  fuming  sulphuric  acid. —  Nordhausen  or  fuming 
sulphuric  acid,  consisting,  as  it  does,  essentially  of  a  solution 
of  sulphur  trioxide  in  sulphuric  acid,  readily  liberates  the 
trioxide  on  heating.  The  fuming  acid  is  placed  in  a  500  cc. 
retort,  whose  neck  is  thrust  into  a  250  cc.  flask  immersed  in  a 
freezing-mixture  of  salt  and  ice.  On  gently  heating  the  acid 
the  sulphuric  trioxide  is  given  off  and  condenses  in  the 
receiver.  Owing  to  the  intensely  corroding  properties  of 
the  acid  the  retort  must  be  very  carefully  heated  to  avoid 
danger  of  breakage.  The  danger  is  minimized  if  a  sand- 
bath  is  used. 

H2S2O7  =  H2SO4  +  SO3. 

500  cc.  retort ;  250  cc.  flask  ;  sand-bath  ;  Nordhausen  sulphuric  acid. 

61.  From  sulphuric    acid  and   phosphorus  pentoxide. — 

Phosphorus  pentoxide  abstracts  water  from  sulphuric  acid, 
setting  free  sulphuric  anhydride. 

A  few  drops  of  strong  sulphuric  acid  are  placed  in  a  test- 
tube,  and  sufficient  phosphorus  pentoxide  is  added  to  make  a 
thin  paste.  On  gently  heating  the  mixture  a  vigorous  reac- 
tion takes  place,  clouds  of  sulphur  trioxide  being  given  off. 

3  H2SO4  +  P2O5  =  2  H3PO4  -f  3  SO3 . 

62.  By  heating  potassium  disulphate.  —  Potassium  di sul- 
phate, when  heated  in  a  test-tube,  forms  potassium  sulphate 
and  sulphur  trioxide. 


SULPHUR   TRIOXIDE  161 

A  bell-jar  whose  sides  have  been  moistened  with  water  is 
held  over  the  test-tube  containing  potassium  disulphate  and 
the  fumes  allowed  to  condense  in  the  bell-jar.  On  washing 
out  the  contents  of  the  jar  into  a  cylinder  and  adding  barium 
chloride  solution,  a  white  precipitate  of  barium  sulphate  will 
be  formed. 

K2SA  =  K2SO4  +  SO3. 

Bell-jar  ;  K2S2O7  ;  BaCl2  solution. 

PROPERTIES 

63.  Action  on  water.  —  (a)  A  bottle  containing  sulphur 
trioxide  fumes  on  removing  the  stopper.  The  fumes  of 
Nordhausen  or  fuming  sulphuric  acid  are  due  to  the  pres- 
ence of  large  quantities  of  the  trioxide. 

The  anhydride  is  very  deliquescent,  and,  when  solid,  is 
best  removed  with  a  glass  rod.  Enough  will  cling  to  the 
rod  to  illustrate  its  properties. 

The  fundamental  precaution,  not  to  pour  water  into  sul- 
phuric acid,  may  be  here  repeated.  The  danger  is  infinitely 
greater  if  water  is  poured  into  a  vessel  containing  sulphur 
trioxide.  The  results  of  such  an  operation  are  seen  in  the 
following  experiments.  The  acid  nature  of  a  solution  of 
sulphur  trioxide  in  water  may  be  shown  by  immersing  a 
piece  of  blue  litmus  paper  in  it. 

SO3  +  H2O  =  H2SO4. 

(b)  The  intensity  of  the  reaction  between  sulphuric  anhy- 
dride and  water  is  so  great  that  the  addition  of  water  to  the 
anhydride  becomes  a  very  dangerous  operation.  On  the 
small  scale,  the  experiment  may  be  made  without  danger,  as 
follows  :  — 

A  small  quantity  of  sulphur  trioxide  is  placed  in  a  plati- 
num crucible,  imbedded  in  a  layer  of  sand,  at  the  bottom  of 


162 


CHEMICAL   LECTURE   EXPERIMENTS 


a  glass  cylinder  (Fig.  70).  A  glass  funnel  is  inserted  in 
the  mouth  of  the  cylinder,  and  its  stem,  which  should  be  as 
long  as  possible,  directed  so  as  to  allow  water 
to  drop  into  the  crucible.  On  pouring  a  few 
drops  of  water  into  the  funnel,  they  will  fall 
upon  the  trioxide  in  the  crucible,  the  union 
taking  place  with  almost  explosive  violence. 

Apparatus  (Fig.   70)  ;    glass  cylinder ;    Pt  crucible  ; 
sand  :  funnel  :  SOa. 


(c)    A  tall  cylinder  is  one-third  filled  with 
^    water  and  a  few  crystals,  or  5  cc.    of  liquid 


Fig.  70        sulphur  trioxide  are  dropped  into  it.     As  each 
particle  comes  in  contact  with  the  water,  there 
is  a   hissing   and   explosion.      The  column  of  air  in  the 
cylinder  intensifies  the  sound. 

Cylinder  one -third  filled  with  water  ;  SO3. 

(d)  A  small  dry  test-tube  is  drawn  out  at  the  middle,  so 
as  to  leave  a  hook  of  glass  at  the  bottom  of  the  upper  part, 
to  which  a  weight  may  be  fastened  (Fig.  71). 
One  cubic  centimeter  of  liquid  sulphur  trioxide, 
or  its  equivalent  amount  in  crystals,  is  placed 
in  the  test-tube  to  which  the  weight  has  been 
fastened.  It  is  then  allowed  to  drop  into  a  tall 
cylinder  containing  about  a  liter  of  water.  The 
cylinder  should  not  be  more  than  three-fourths 
full.  As  the  tube  sinks  beneath  the  surface  of 
the  water,  the  sulphur  trioxide  unites  with  the 
water  with  explosive  violence. 

drawn-out  test-tube  with  weight ;  liter  cyl- 


Gauntlets 
inder  :  SO3. 


Fig.  71 


64.    Action  of  sulphur.  —  Sulphur  dissolves  in  sulphur  tri- 
oxide to  form  a  blue  liquid,  tlie  so-called  sulphur  sesquioxide. 


SULPHUR   TRIOXIDE  163 

On  standing,  the  liquid  decomposes,  loses  its  blue  color,  and 
forms  sulphur  dioxide. 

A  small  quantity  of  sulphur  trioxide  is  placed  in  a  dry 
test-tube,  and  a  very  small  pinch,  of  sulphur  flowers  added 
to  it.  The  solution  becomes  blue,  but  by  gently  warming, 
the  color  disappears,  and  a  paper  moistened  in  potassium 
dichromate  solution  indicates  the  presence  of  sulphur 
dioxide.  so,  +  S  =  SA.     [?] 

Sulphur  trioxide  ;  S  flowers. 

65.  Action  with  phosphorus.  —  Phosphorus  reduces  sul- 
phur trioxide,  with  the  liberation  of  sulphur  dioxide. 

Two  cubic  centimeters  of  liquid  sulphur  trioxide  are  placed 
in  a  dry  test-tube,  and  a  5  mm.  piece  of  well-dried  phos- 
phorus is  added.  The  phosphorus  catches  fire  of  itself  and 
burns  on  the  surface  of  the  liquid,  obtaining  its  oxygen 
from  the  sulphur  trioxide.  Large  quantities  of  sulphur 
dioxide  are  evolved.  The  residue  in  the  test-tube  at  the 
end  of  the  reaction  may  be  carefully  immersed  in  a  large 
cylinder  of  water,  and  it  will  be  seen  that  the  phosphorus 
has  all  been  oxidized,  as  there  will  be  little,  if  any,  insoluble 
matter  in  the  residue.  Owing  to  the  fumes  evolved,  it  is 
better  to  conduct  the  experiment  under  the  hood. 

5  SO3  -f  2  P  =  P2O5  +  5  SO2. 
SOs ;  P. 

66.  Action  with  barium  oxide.  —  Barium  oxide  combines 
with  sulphur  trioxide  to  form  barium  sulphate. 

A  small  quantity  of  sulphur  trioxide  is  placed  in  a  dry 
test-tube,  and  powdered  barium  oxide  carefully  sifted  into 
the  tube.  The  union  of  the  two  compounds  is  accompanied 
by  an  evolution  of  heat  and  light. 

BaO  +  SO3  =  BaSO^. 
Screens ;  gauntlets ;  barium  oxide  ;  sulphur  trioxide. 


164 


CHEMICAL  LECTURE  EXPERIMENTS 


SULPHURIC   ACID 

FORMATION   AND   PREPARATION 

67.  By  the  oxidation  of  sulphur  with  nitric  acid.  —  Sul- 
phur, when  heated  with  fuming  nitric  acid,  is  oxidized  to 
sulphuric  acid. 

Two  grams  of  sulphur  flowers  are  heated  to  boiling  in  a 
100  cc.  Erlenmeyer  flask  with  10  cc.  of  fuming  nitric  acid. 
On  diluting  the  mixture  with  water  and  pouring  it  upon 
a  filter,  the  filtrate  will  be  found  to  contain  considerable 
free  sulphuric  acid,  which  will  give  a  white  precipitate  with 
barium  chloride. 

S  flowers  ;  fuming  HNOs. 

68.  By  the  action  of  nitric  acid  on  sulphur  dioxide.  —  Sul- 
phur dioxide,  when  conducted  into  concentrated  nitric  acid, 
becomes  oxidized,  forming  sulphuric  acid  and  setting  free 

nitrogen  peroxide.  In 
^^^ — (^^  case  dilute  nitric  acid 
is  used,  nitric  oxide 
rather  than  nitrogen 
peroxide   is   liberated. 

A  current  of  sulphur 
dioxide     is     conducted 
into  a  300  cc.  flask  con- 
taining  75  cc.  of   con- 
centrated   nitric    acid. 
The  cork  of  the   flask 
is    provided    with    two 
holes,   through    one   of 
which  the   sulphur  di- 
oxide is  conducted,  while  the  other  allows  for  the  escape 
of  the  nitrogen  peroxide  formed.     An  elbow  in  the  second 
hole  conducts  the  nitrogen  peroxide  to  the  bottom  of  an 


Fig.  72 


SULPHURIC   ACID  165 

empty  glass  cylinder  fitted  with  a  two-holed  cork  (Fig.  72). 
All  connections  should  be  made  with  the  glass  tubes  as 
nearly  touching  each  other  as  possible,  since  the  nitrogen 
peroxide  fumes  attack  rubber.  On  conducting  sulphur 
dioxide  into  the  nitric  acid,  the  liquid  warms  up  of  itself 
and  deep  reddish-brown  fumes  of  nitrogen  peroxide  escape 
and  fill  the  glass  cylinder.  After  a  few  moments  the  liquid 
in  the  flask  may  be  diluted  with  water  and  tested  for  the 
presence  of  sulphuric  acid  by  means  of  barium  chloride. 

If  the  concentrated  nitric  acid  in  the  apparatus  is  replaced 
by  an  acid  of  the  specific  gravity  of  1.15  and  the  experi- 
ment repeated,  it  will  be  found  that  the  gas  escaping  into 
the  glass  cylinder,  while  somewhat  colored,  consists  chiefly 
of  nitric  oxide,  as  can  be  seen  by  opening  the  mouth  of  the 
cylinder  and  allowing  the  gas  to  come  in  contact  with  the 
air.  The  formation  of  red  fumes  indicates  the  presence  of 
nitric  oxide.  It  will  be  found  necessary  to  warm  the  dilute 
nitric  acid  somewhat  in  order  to  start  the  reaction.  At  the 
end  of  the  experiment,  the  liquid  may  be  tested  as  before 
for  sulphuric  acid. 

SO2  4-  2  HNO3  =  H2SO4  +  2  NO2. 

3  SO2  4-  2  HNO3  +  2  H2O  =  3  H2SO4  +  2  NO. 

Flask  with  2-holed  cork  ;  glass  cylinder  ;  SO2  generator ;  HNOs 
(sp.  gr.  1.15)  ;  con.  HNO3. 

69.  Chamber  crystals  by  the  action  of  concentrated  nitric 
acid  on  sulphur  dioxide.  —  Nitric  acid  oxidizes  sulphur  diox- 
ide, forming  sulphuric  acid. 

A  piece  of  asbestos  paper  fastened  to  a  wire  is  dipped 
into  concentrated  nitric  acid  and  lowered  into  a  cylinder  of 
sulphur  dioxide.  A  marked  reaction,  filling  the  jar  with 
red  fumes,  is  observed.  The  walls  of  the  cylinder  soon 
become  coated  with  chamber  crystals. 

Jar  of  SO2 ;  con.  HNOa. 


166 


CHEMICAL   LECTURE   EXPERIMENTS 


70.  By  the  oxidation  of  sulphur  dioxide  by  means  of  nitric 
oxide  in  the  presence  of  air  and  water  vapor.  —  In  the  manu- 
facture of  sulphuric  acid  on  a  large  scale  the  oxidation  of 
sulphur  dioxide  is  effected  by  means  of  nitric  oxide  in  the 
presence  of  air.  On  the  lecture-table  the  substitution  of  a 
gaseous  for  a  liquid  oxidizing  agent  may  be  successfully 
carried  out  by  conducting  the  gaseous  compounds,  i.e.  sul- 
phur dioxide,  nitric  oxide,  air,  and  water  vapor,  into  a  large 
flask,  where  the  reaction  takes  place. 

A  4  or  5  1.  flask  is  provided  with  a  four-holed  cork, 
through  three  holes  of  which  glass  tubes  are  thrust  about 
halfway  to  the  bottom  of  the  flask.  In 
the  fourth  hole  a  short  glass  elbow  is 
inserted,  which  connects  with  a  flue 
(Fig.  73).  The  flask  must  be  per- 
fectly dry  and  is  first  filled  with  nitric 
oxide  from  a  generator,  consisting  of  a 
300  cc.  Erlenmeyer  flask,  fitted  with  a 
thistle-tube  and  a  glass  elbow.  A  layer 
of  copper  turnings  is  placed  in  the 
bottom  of  the  generator  and  sufficient 
water  added  to  cover  them.  Concen- 
trated nitric  acid  is  poured  through 
the  thistle-tube,  and  soon  the  reaction 
begins.  The  colorless  nitric  oxide  com- 
bines with  the  oxygen  of  the  air  in  the 
large  flask,  filling  it  with  deep  ruddy 
fumes  of  nitrogen  peroxide.  At  this 
point  the  evolution  of  nitric  oxide  is 
stopped  by  pouring  water  into  the  nitric  oxide  generator. 
If  it  is  desirable  to  start  the  action  again,  it  is  only  neces- 
sary to  add  a  little  more  concentrated  nitric  acid. 

The  second  tube  in  the  cork  of  the  large  flask  is  con- 
nected with  a  sulphur  dioxide  generator,  such   as   is   de- 


FiG.  73 


SULPHURIC    ACID  167 

scribed  in  Ex.  41.  The  sulphur  dioxide  is  first  conducted 
through  a  gas  washing-bottle  containing  a  small  amount  of 
water  to  note  the  rapidity  of  its  evolution.  A  vigorous 
stream  of  sulphur  dioxide  is  then  allowed  to  flow  into  the 
flask  for  two  or  three  minutes.  The  third  tube  in  the  cork 
of  the  flask  is  connected  with  a  100  cc.  Erlenmeyer  flask 
containing  25  cc.  of  water  and  so  provided  with  a  cork  and 
glass  elbows  that  a  stream  of  air  may  be  blown  through  the 
water  into  the  large  flask.  During  the  previous  operations 
the  water  is  brought  almost  to  a  boil.  After  the  current  of 
sulphur  dioxide  is  stopped  air  is  blown  through  the  hot 
water,  thereby  carrying  a  small  amount  of  moisture  into  the 
chamber.  If  care  is  taken  not  to  admit  too  great  a  quantity 
of  moisture,  the  sulphur  dioxide  and  nitrogen  peroxide  will 
interact  with  the  small  amount  of  water,  and  the  sides  of 
the  vessel  will  become  covered  with  crystals,  the  so-called 
"  chamber  crystals." 

The  decomposition  of  the  chamber  crystals  and  the 
regeneration  of  the  nitrogen  j)eroxide  are  effected  by  pass- 
ing into  the  flask  considerable  quantities  of  water  vapor. 
The  contents  of  the  small  flask  are  vigorously  boiled,  and 
the  steam  escapes  into  the  large  flask.  The  tube  through 
which  air  is  conducted,  dipping  under  the  surface  of  the 
water  in  the  small  flask,  is  sealed,  and  the  steam  is  thus 
prevented  from  escaping  into  the  air  of  the  room.  After 
the  steam  has  entered  the  large  flask  for  a  few  moments, 
the  crystals  are  rapidly  decomposed  with  effervescence, 
nitric  oxide  being  liberated.  By  blowing  air  into  the 
flask,  its  contents  once  more  become  red  from  the  formation 
of  nitrogen  peroxide.  If  sulphur  dioxide  is  now  conducted 
into  the  flask,  the  red  fumes  will  disappear,  but  the  excess 
of  moisture  in  the  flask  will  probably  prevent  the  reappear- 
ance of  the  chamber  crystals. 

In  case  the  flask  becomes  too  warm  from  the  reaction,  the 


168  CHEMICAL   LECTURE   EXPERIMENTS 

formation  of  chamber  crystals  may  be  somewhat  accelerated 
by  cooling  the  outside  of  the  flask  with  a  cloth  wet  with 
cold  water.  When  the  crystals  are  once  started,  they 
spread  .with  considerable  rapidity  all  over  the  surface  of 
the  flask. 

If  the  formation  of  sulphuric  acid  only  is  desired,  and  the 
introduction  of  chamber  crystals  avoided,  it  is  only  neces- 
sary to  conduct  simultaneously  into  the  large  flask  nitric 
oxide,  sulphur  dioxide,  water  vapor,  and  air.  On  adding 
water  and  pouring  out  the  contents  of  the  flask,  they  will 
be  found  to  give  a  strong  test  for  sulphuric  acid  with  barium 
chloride. 

SO2  +  H2O  +  NO2  =  nSOi  +  NO. 

2NO  +  02  =  2N02. 

/O  •  NO. 
4  SO2  +  4  NO2  +  O2  +  2  H2O  =  4  S02< 

\0H. 

4  or  5  1.  flask  ;  4-holed  cork  and  tubes  ;  SO2  generator  ;  NO  gen- 
erator ;  steam  generator, 

71.  From  sulphur  dioxide,  fuming  nitric  acid,  air,  and 
water  vapor.  —  The  technical  manufacture  of  sulphuric  acid 
is  considered  of  sufficient  importance  to  demand  a  special 
and  elaborate  treatment  in  most  text-books  on  chemistry. 
It  is  desirable,  therefore,  to  present  on  the  lecture-table  a 
demonstration  of  the  technical  process  for  the  manufacture 
of  this  acid,  which  shall  not  be  too  elaborate  and  yet  shall 
be  sufficiently  detailed  to  show  the  essential  steps.  While 
the  fundamental  reactions  are  admirably  illustrated  in  the 
apparatus  described  in  the  preceding  experiment,  a  number 
of  technical  features  of  economic  importance  warrant  illus- 
trative consideration  on  the  lecture-table,  and  accordingly 
the  apparatus  shown  in  Fig.  74  has  been  devised  for  this 
purpose. 


SULPHURIC    ACID 


169 


The  chamber  consists  of  a  2  or  3  1.  three-necked  Wolff 
bottle,  through  the  middle  neck  of  which 
is  inserted  a  two-holed  rubber  stopper  car- 
rying a  dropping-funnel  and  a  glass  elbow. 
The  other  two  necks  are  provided  with  one- 
holed  rubber  stoppers  carrying  glass  tubes 
of  the  special  form  indicated  in  the  figure. 
Two  Liebig  condenser  jackets  filled  with 


3*- 


Fig.  74 


broken  bits  of  pumice-stone  serve  as  the  Gay-Lussac  and 
Glover  towers,  respectively.     The  condenser  jackets  should 


170  CHEMICAL  LECTURE   EXPERIMENTS 

have  the  water-tubes  on  opposite  sides  if  possible,  as  other- 
wise it  will  be  necessary  to  bend  glass  tubes  to  make  the 
proper  connections.  One  of  the  condensers  is  clamped 
in  an  upright  position,  its  lower  end  dipping  into  a  small 
beaker  one-third  filled  with  concentrated  sulphuric  acid.  A 
piece  of  combustion-tube  25  cm.  long  is  fastened  to  the 
lower  water-tube  of  the  condenser  by  means  of  a  rubber 
stopper,  and  a  small  plug  of  glass  wool  is  thrust  into  the 
combustion-tube.  A  porcelain  boat,  filled  with  bits  of  roll 
sulphur  of  such  a  size  as  can  conveniently  pass  into  the 
combustion-tube,  is  inserted  part  way  in  the  tube.  In  case 
the  combustion-tube  does  not  remain  in  a  level  position,  it 
may  be  necessary  to  support  it  with  a  ring  from  the  large 
retort  stand. 

The  upper  water-tube  of  the  condenser  is  connected  by 
a  long  glass  elbow  to  one  of  the  necks  of  the  Wolff  bottle. 
The  second  condenser  jacket  is  clamped  in  a  vertical  position 
on  the  other  side  of  the  Wolff  bottle,  in  such  a  manner  that 
its  lower  end  will  be  3  or  4  cm.  higher  than  the  upper  end  of 
the  other  condenser.  The  two  condensers  are  connected 
by  a  long,  small-bored  glass  tube,  thrust  through  the  corks 
inserted  in  the  end  of  the  condensers.  The  glass  tube 
should  extend  several  millimeters  below  the  cork  in  the  top 
of  the  lower  condenser,  and  should  be  just  flush  with  the 
end  of  the  cork  thrust  into  the  lower  end  of  the  upper  con- 
denser. As  this  cork  is  subject  to  the  action  of  concentrated 
sulphuric  acid,  it  is  best  to  coat  it  with  paraffin  and  thrust 
it,  while  still  warm,  into  the  condenser.  Care  should  be 
taken  in  coating  the  cork  that  the  paraffin  does  not  seal  the 
glass  tube  by  running  into  it  and  solidifying.  The  lower 
water-tube  of  the  upper  condenser  is  connected  with  a  long 
glass  elbow  to  the  third  neck  of  the  Wolff  bottle.  The  upper 
water-tube  is  connected  with  a  suction-pump,  a  gas  washing- 
bottle  containing  water  being  inserted  at  some  point  between 


SULPHURIC   ACID  171 

the  condenser  tube  and  the  pump.  A  one-holed  rubber 
stopper,  carrying  a  dropping-funnel  filled  with  concentrated 
sulphuric  acid,  is  inserted  in  the  upper  end  of  the  upper  con- 
denser. Concentrated  sulphuric  acid  is  allowed  to  flow  down 
over  the  pumice-stone  in  the  upper  condenser,  which  it  thor- 
oughly drenches.  The  acid  collects  in  the  bottom  of  the 
condenser  and  flows  through  the  small  tube  into  the  lower 
condenser,  trickling  down  over  the  pumice-stone,  and  finally 
is  collected  in  the  beaker. 

The  following  arrangement  is  provided  for  sending  water 
vapor  through  the  glass  elbow  in  the  middle  neck  of  the 
Wolff  bottle.  A  100  cc.  Erlenmeyer  flask,  one-fourth  filled 
with  water,  is  fitted  with  a  two-holed  rubber  stopper.  A 
glass  elbow,  7  mm.  in  diameter,  is  thrust  through  one  hole 
in  the  cork,  and  a  small  glass  elbow,  2  mm.  in  diameter,  is 
thrust  through  the  second  hole.  The  large  elbow  carries  a 
piece  of  rubber  tubing  and  a  pinch-cock.  The  small  elbow 
is  connected  with  the  elbow  leading  into  the  middle  neck  of 
the  Wolff  bottle.  The  flask  is  supported  on  a  stand  and 
gently  warmed  with  a  Bunsen  burner,  the  water  being  kept 
at  or  near  boiling.  The  pinch-cock  should  be  moved  up  on 
the  glass  elbow,  thus  allowing  free  escape  for  the  water 
vapor  through  the  large  glass  elbow  and  the  rubber  tube. 
Steam  condenses  in  one  end  of  the  small  glass  elbow,  and 
the  drop  clinging  to  the  end  of  the  tube  prevents  the  escape 
of  the  steam  into  the  Wolff  bottle.  When  it  is  desired  to 
introduce  steam  into  the  acid  chamber,  the  flame  is  raised 
and  the  water  in  the  flask  brought  to  a  vigorous  boil.  By 
closing  the  rubber  tube  on  the  large  elbow  with  the  pinch- 
cock,  the  steam  forces  its  way  through  the  small  elbow  into 
the  acid  chamber.  On  releasing  the  pinch-cock,  the  steam 
issues  from  the  large  elbow  into  the  air  of  the  room,  as  before. 
A  few  bits  of  pumice-stone  or  glass  beads  promote  the  regu- 
larity of  ebullition. 


172  CHEMICAL  LECTURE  EXPERIMENTS 

The  preparation  of  sulphuric  acid  by  means  of  this  appa- 
ratus is  extremely  simple.  Ten  to  fifteen  drops  of  fuming 
nitric  acid  are  allowed  to  fall  into  the  Wolff  bottle,  which 
should  be  perfectly  dry.  If  the  stem  of  the  dropping-funnel 
has  been  previously  filled  with  acid,  the  regulation  of  the 
dropping  will  be  much  simplified.  The  boat  containing  sul- 
phur is  then  drawn  halfway  out  of  the  tube,  and  the  sulphur 
strongly  ignited  by  heating  with  a  lamp.  When  burning 
well,  the  suction  is  started  and  air  drawn  through  the  com- 
bustion-tube over  the  burning  sulphur  into  the  apparatus. 
After  the  current  of  air  is  started,  it  is  necessary  to  maintain 
it  at  a  rate  just  sufficient  to  draw  the  flame  of  the  burning 
sulphur  into  the  combustion-tube.  In  this  manner  a  mixture 
of  air  and  sulphur  dioxide  is  carried  into  the  chamber. 
After  a  few  moments  the  walls  of  the  flask  will  become 
covered  with  a  deposit  of  chamber  crystals.  Water  vapor  is 
then  admitted,  and  consequently  the  chamber  crystals  are 
decomposed  with  the  liberation  of  nitrous  fumes. 

The  formation  of  chamber  crystals,  being  dependent  on  a 
certain  proportion  of  water,  nitric  oxide,  and  sulphuric  acid, 
is  a  matter  of  considerable  difliculty,  and  cannot  always  be 
relied  on.  When  the  operation  is  carried  out  as  described, 
however,  the  chamber  crystals  are,  as  a  rule,  readily  obtained. 

The  interaction  of  the  various  products  in  the  acid  cham- 
ber is  accompanied  by  a  formation  of  fumes,  showing  that 
chemical  reaction  has  taken  place.  On  disconnecting  the 
tubes  and  removing  the  Wolff  bottle,  it  will  be  found  that 
the  contents  diluted  with  water  will  give  a  strong  test  for 
sulphuric  acid.  When  sulphur  is  burned  in  this  manner  a 
portion  of  it  sublimes,  but  it  is  retained  by  the  glass  wool 
in  the  combustion-tube.  The  current  of  air  entering  the 
combustion-tube  passes  through  the  Glover  tower  into  the 
chamber.  Any  nitrogen  oxides  carried  away  by  the  current 
of  air  are  absorbed  by  the  sulphuric  acid  in  the  Gay-Lussac 


SULPHURIC   ACID  173 

tower.  The  acid  containing  the  nitrogen  fumes  flows  down 
through  the  long  glass  tube  into  the  upper  end  of  the  Glover 
tower,  where,  in  trickling  down  over  the  pumice-stone,  it 
comes  in  contact  with  the  sulphur  dioxide,  which  reacts 
with  it,  setting  free  the  nitrogen  oxides. 

While  the  actual  absorption  of  the  nitrogen  oxides  in  the 
Gay-Lussac  tower,  and  their  subsequent  regeneration  in  the 
Glover  tower,  cannot  be  observed,  the  process  is  interesting 
as  being  a  duplicate  of  that  used  in  the  commercial  manu- 
facture of  this  acid.  The  supply  of  sulphuric  acid  in  the 
dropping-funnel  in  the  top  of  the  Gay-Lussac  tower  should 
occasionally  be  replenished,  as  the  acid  should  continuously 
drop  upon  the  pumice-stone. 

Obviously,  nitric  oxide,  instead  of  fuming  nitric  acid,  may 
be  conducted  through  the  middle  neck,  in  case  the  gaseous 
oxidizing  agent  is  desired. 

Apparatus  (Fig.  74)  ;  3-necked  Wolff  bottle  ;  two  Liebig  con- 
denser jackets  filled  with  pumice-stone  ;  dropping-funnel ;  porcelain 
boat ;  combustion-tube  ;  glass  wool ;  steam  generator ;  suction-pump  ; 
S;  fuming  HNO3. 

PROPERTIES 

72.  Intense  acidity.  —  The  intense  acid  nature  of  sul- 
phuric acid  is  shown  by  adding  1  drop  of  the  concentrated 
acid  to  2  1.  of  water  in  a  large  beaker.  It  will  be  found  that 
the  water  is  acid  enough  to  redden  a  strip  of  blue  litmus. 

2  1.  beaker  ;  blue  litmus  paper. 

73.  Evolution  of  heat  by  mixing  sulphuric  acid  with 
water.  —  (a)  When  sulphuric  acid  and  water  are  mixed, 
there  is  considerable  rise  in  temperature,  sufficient  to  boil 
ether. 

Two  hundred  cubic  centimeters  of  water  are  placed  in  a 
500  cc.  flask,  and  5  cc.  of  ether  are  added.     On  holding  a 


174 


CHEMICAL   LECTURE   EXPERIMENTS 


Fig.  75 


match  at  the  mouth  of  the  flask  no  flame  will  appear.     On 
the  addition  of  100  cc.  of  concentrated  sulphuric  acid  the 
temperature  of  the  mixture  is  so  increased  that  the  ether 
boils  vigorously,  and  the  issuing  vapor  may- 
be ignited  at  the  mouth  of  the  flask. 

After  the  flame  has  gone  out,  an  ether 
thermometer,  made  by  blowing  an  8  or 
10  mm.  bulb  on  the  end  of  a  long  piece  of 
3  mm.  glass  tubing,  is  half  filled  with  ether, 
and  the  bulb  thrust  into  the  hot  mixture 
of  acid  and  water  (Fig.  75).  The  ether 
boils  vigorously,  and  on  applying  a  flame 
burning  ether  vapor  issues  from  the  mouth 
of  the  tube 

500  cc.  flask  ;  long  tube  with  bulb  ;  ether. 

(b)  The  evolution  of  heat,  on  mixing  these  two  liquids, 
is  sufficient  to  give  a  temperature  to  the  mixture  of  consid- 
erably over  100°.  Sixty  cubic  centimeters  of  water  and 
120  cc.  of  concentrated  sulphuric  acid  are  simultaneously 
poured  (to  insure  thorough  mixing)  into  a  300  cc.  beaker 
standing  on  wire  gauze  or  asbestos  paper.  A  thermometer 
inserted  in  the  mixture  will  indicate  a  temperature  of  115° 
to  120°. 

A  small  quantity  of  alcohol  in  a  thin-walled  test-tube  is 
immersed  in  the  hot  liquid.  The  alcohol  boils,  and  the  vapor 
may  be  ignited  at  the  mouth  of  the  tube. 

Two  cubic  centimeters  of  water  in  a  thin-walled  test-tube 
may  be  quickly  brought  to  a  boil  by  immersing  the  tube  in 
the  hot  solution. 

300  cc.  beaker  ;  gauze  ;  thin- walled  test-tubes  ;  120  cc.  con.  H2SO4; 
alcohol. 

74.  Dehydrating  action  (drying  of  gases).  —  Sulphuric 
acid,  owing  to  its  intense  hygroscopic  properties,  is  of  the 


SULPHURIC    ACID 


175 


greatest  importance  in  drying  many  gases.  The  interior 
surface  of  a  bell-jar  is  moistened  by  holding  it  over  a 
Bunsen  or,  better,  a  hydrogen  flame.  A  small  evaporating 
dish  filled  with  lump  pumice- 
stone,  which  has  been  drenched 
with  sulphuric  acid,  is  placed 
on  a  plate  under  the  moistened 
bell-jar  (Fig.  76).  In  a  few  min- 
utes the  walls  of  the  jar  will  be- 
come clear  and  unclouded  as  the 

water  vapor  is  rapidly  absorbed  by  the  sulphuric  acid.  The 
rapidity  of  the  absorption  is  still  more  emphasized  by  pre- 
paring a  second  bell- jar  as  before  and  placing  it  over  pumice- 
stone  drenched  with  water.  In  the  second  case  the  bell-jar 
remains  clouded  with  the  condensed  water  vapor. 

H  flame  ;  2  bell-jars ;  2  evaporating  dishes  ;  2  plates  ;  pumice-stone. 

75.  Carbonization  of  sugar  by  sulphuric  acid.  —  Sixty 
grams  of  lump  sugar  are  added  to  45  cc.  of  warm  water  in 
a  500  cc.  beaker.  The  sugar  will  soon  dissolve  in  the  water, 
forming  a  thick  syrup.  The  beaker  is  placed  on  a  white 
plate  and  60  cc.  of  concentrated  sulphuric  acid  rapidly 
poured  into  it.  The  reaction  is  almost  instantaneous,  the 
solution  blackening,  and  large  quantities  of  steam  being 
driven  off.  The  residue  is  a  porous,  carbonaceous  mass. 
The  mixture  will  froth  up  and  run  over  the  edge  of  the 
beaker  upon  the  plate. 

500  cc.  beaker  ;  lump  sugar. 

76.  Action  on  paper.  —  Dilute  sulphuric  acid  has  no  ap- 
preciable effect  on  paper,  but  if  paper  moistened  with  dilute 
acid  is  gently  warmed,  the  water  is  vaporized,  leaving  the 
non-volatile  sulphuric  acid. 

A  dilute  sulphuric  acid  is  made  by  adding  10  cc.  of  con- 


176      CHEMICAL  LECTURE  EXPERIMENTS 

centrated  sulphuric  acid  to  250  cc.  of  water.  A  letter  is 
made  on  paper  with  this  dilute  acid,  and  the  paper  then 
allowed  to  dry  in  the  air.  When  perfectly  dry  no  change 
is  noticeable.  If  the  paper  is  held  high  over  a  Bunsen  flame 
and  simply  warmed,  the  acid,  concentrated  by  evaporation, 
will  carbonize  all  portions  of  the  paper  with  which  it  is  in 
contact,  and  the  character  will  appear  in  a  charred  outline. 


SELENIUM 


SELENIUM 


1.  Sublimation.  —  Selenium,  when  heated,  sublimes  with- 
out melting. 

A  small  piece  of  selenium  is  heated  in  a  dry  test-tube. 
The  element  sublimes,  and  the  upper  part  of  the  sublimate 
will  consist  of  fine  needles  of  selenium  dioxide  formed  by 
the  combustion  of  the  vapor  in  the  air  of  the  tube. 

2.  Combustion  in  air.  —  Selenium,  when  heated  in  the  air, 
burns  with  a  blue  flame,  forming  selenium  dioxide. 

A  small  piece  of  selenium  is  heated  on  a  crucible  cover 
and  ignited.  It  burns  with  a  characteristic  blue  flame,  but 
it  is  necessary  to  keep  the  crucible  cover  heated  during  the 
combustion. 

Crucible  cover ;  Se. 

3.  Solubility  in  strong  sulphuric  acid.  —  (a)  Powdered 
selenium  is  covered  in  a  test-tube  with  fuming  sulphuric 
acid  and  strongly  heated.  The  selenium  dissolves  with  the 
liberation  of  sulphur  dioxide.  The  sulphuric  acid  con- 
taining selenious  acid  becomes  green.  The  green  solution 
is  carefully  poured  into  a  300  cc.  cylinder  half  filled  with 
cold  water.  Selenium  separates  out  of  the  solution  in  the 
form  of  a  fine,  dark  red  powder. 

Se  ;  fuming  H2SO4  ;  K2Cr207  solution. 
N  177 


178 


CHEMICAL  LECTURE  EXPERIMENTS 


(b)  Selenium,  when  heated  with  fuming  sulphuric  acid, 
dissolves  with  a  green  color.  If  the  solution  is  then  diluted 
with  concentrated  sulphuric  acid  and  heated  to  boiling  for  a 
few  moments,  it  will  finally  be  decolorized  as  the  selenium 
is  oxidized  by  the  sulphur  trioxide.  On  pouring  the  de- 
colorized solution  into  water  no  precipitate  of  selenium  will 
occur.  2  SO3  +  Se  =  2  SO^  +  SeO^. 

Fuming  H2SO4 ;  Se. 

SELENIUM   DIOXIDE 

4.  Preparation.  —  Selenium  burns  in  a  current  of  oxygen  to 
form  selenium  dioxide.  A  few  lumps  of  selenium  are  placed 
in  a  bulb-tube,  which  is  fitted  to  the  mouth  of  a  dry  filter- 
flask,  the  side  tube  of  which  is 
connected  with  a  flue  (Fig.  77). 
A  current  of  oxygen  is  passed 
through  the  bulb- tube  and  the 
selenium  heated  to  ignition. 
The  product  condenses  on  the 
arm  of  the  tube  and  in  the  re- 
ceiver as  a  white  powder. 

Se  +  02  =  Se02. 


Fia.  T7 


Apparatus  (Fig.  77)  ;  bulb-tube 
filter  flask  ;  0  supply  ;  Se. 


5.  Green  color  of  the  vapor.  —  A  small  quantity  of  selenium 
dioxide  is  heated  in  a  test-tube.  The  greenish  vapor  is  best 
seen  by  holding  the  tube  in  front  of  a  white  background. 


SELENIOUS   ACID 

6.  Oxidation  of  selenium  with  nitric  acid.  —  When  pow- 
dered selenium  is  heated  in  a  test-tube  with  concentrated 
nitric  acid,  it  rapidly  dissolves,  with  the  liberation  of  nitrous 


SELENIC    ACID  179 

fumes,  forming  selenious  acid.  After  neutralization  with 
ammonia  the  solution  gives  any  of  the  reactions  for  seleni- 
ous acid. 

7.  By  dissolving  selenium  dioxide  in  water.  —  Selenium 
dioxide  dissolves  readily  in  water,  forming  selenious  acid. 
The  aqueous  solution  may  be  used  in  the  following  experi- 
ments. 

8.  Action  with  hydrogen  sulphide.  —  Hydrogen  sulphide 
solution,  when  added  to  a  solution  of  selenious  acid,  pro- 
duces a  bright  yellow  precipitate  of  selenium  sulphide. 

9.  Reduction  by  sulphurous  acid.  —  Sulphurous  acid  re- 
duces selenious  acid  to  selenium.  Sulphur  dioxide,  or  a 
solution  of  sulphur  dioxide  in  water,  is  added  to  a  dilute 
solution  of  selenious  acid.  In  the  cold,  or  more  rapidly  by 
warming,  a  brick-red  precipitate  of  finely  divided  selenium 
is  obtained. 

H2Se03  +  2  SO2  +  H2O  =  2  H2SO4  +  Se. 

H2SO3  ;  HaSeOg. 

SELENIC   ACID 

10.  Preparation.  —  Chlorine  water  oxidizes  selenium  diox- 
ide to  selenic  acid. 

Selenium  dioxide  is  covered  with  chlorine  water  and 
gently  warmed ;  sufficient  chlorine  water  should  be  added 
to  complete  the  oxidation,  and,  on  boiling  off  the  excess  of 
chlorine,  selenic  acid  is  obtained. 

SeOa  +  CI2  +  2  H2O  =  HaSeO,  +  2  HCl. 
Se02 ;  chlorine  water. 


NITROGEN 


NITROGEN 

PREPARATION 

1.  By  the  decomposition  of  ammonium  chloride  and 
sodium  nitrite.  —  The  decomposition  of  ammonium  nitrite 
results  in  the  formation  of  nitrogen  and  water  according  to 
equation  (1)  below.  The  instability  of  ammonium  nitrite 
precludes  its  use  in  the  pure  state  for  this  reaction,  hence  it 
is  prepared  and  instantly  decomposed  by  using  ammonium 
chloride  and  sodium  nitrite,  whose  interaction  produces 
sodium  chloride  and  ammonium  nitrite,  equation  (2). 

A  mixture  of  10  g.  of  ammonium  chloride  and  15  g. 
of  sodium  nitrite  is  placed  in  a  200  cc.  Erlenmeyer  flask 
fitted  with  a  thistle-tube  and  a  delivery-tube.  Thirty  cubic 
centimeters  of  water  are  then  added  and  the  flask  gently 
heated.  The  nitrogen  is  liberated  considerably  below  the 
boiling  point  of  water,  and  it  is  advisable  not  to  overheat 
the  mixture,  as  frothing  is  likely  to  occur.  In  case  the 
frothing  is  too  strong,  the  introduction  of  a  few  cubic  cen- 
timeters of  water  through  the  thistle-tube  will  immediately 
check  it.  Nitrogen  may  be  collected  at  the  pneumatic 
trough  in  cylinders. 

(1)  NH4NO2  =  N2  +  2  H2O. 

(2)  NaNOa  +  NH4CI  =  NaCl  -f  NH4NO2. 

200  cc.  Erlenmeyer  flask  ;  thistle-tube  and  delivery-tube  ;  NH4CI ; 
NaNOa. 

180 


NITROGEN  181 

2.  By  the  ignition  of  a  mixture  of  ammonium  chloride  and 
potassium  dichromate.  —  The  decomposition  of  ammonium 
dichromate  yielding  nitrogen,  water,  and  chromic  oxide  is 
described  in  Ex.  6,  p.  361.  As  ammonium  dichromate  is 
rather  deliquescent  and  not  common  in  the  laboratory,  the 
same  results  may  be  obtained  by  using  a  mixture  of  ammo- 
nium chloride  and  potassium  dichromate. 

Eight  grams  of  powdered  ammonium  chloride  and  25  g. 
of  powdered  potassium  dichromate  are  intimately  mixed 
and  placed  in  a  100  cc.  Jena  glass  Erlenmeyer  flask.  The 
flask  is  fitted  with  a  very  wide  deli  very -tube,  preferably 
1  cm.  internal  diameter,  which  leads  to  a  pneumatic 
trough  (Fig.  128,  p.  319).  On  heating  the  mixture  nitrogen 
is  evolved  and  some  of  the  ammonium  chloride  is  sublimed, 
hence  the  necessity  of  a  wide  delivery-tube.  The  Jena 
glass  flask  will  stand  a  very  high  heat  without  danger. 

2  NH4CI  +  KsCr^Oy  =  2  KCl  4-  CrA  -f  4  H2O  +  Ng. 

100  cc.  Jena  glass  Erlenmeyer  flask  ;  wide  delivery-tube  ;  K2Cr207; 
NH4CI. 

3.  From  potassium  nitrate  and  iron  powder.  —  Iron  pow- 
der combines  with  the  oxygen  of  potassium  nitrate,  liberat- 
ing nitrogen. 

A  mixture  of  10  g.  of  iron  filings  and  .5  g.  of  pow- 
dered potassium  nitrate  is  heated  in  a  hard-glass  test- 
tube  fitted  with  a  delivery-tube  leading  to  the  pneumatic 
trough.  When  the  mixture  is  heated,  a  gas  is  rapidly  evolved 
which  on  testing  is  shown  to  be  nitrogen. 

Hard-glass  test-tube  ;  cork  and  delivery-tube  ;  KNO3  ;  Fe  powder. 

4.  By  abstraction  of  oxygen  from  air  by  means  of  phos- 
phorus. —  The  commonest  source  of  nitrogen  is  air,  which 
consists   essentially  of  nitrogen   mixed  with  oxygen.     To 


182  CHEMICAL  LECTURE   EXPERIMENTS 

remove  the   oxygen   some   material,    such   as   phosphorus, 
which  forms  a  solid  or  non-gaseous  oxide,  is  selected. 

A  flat  cork,  some  2.5  or  3  cm.  in  diameter  and  a  centime- 
ter thick,  has  the  ring  of  a  porcelain  crucible  lid  pressed 
into  a  slit  in  one  side,  and  on  the  other  side  a  small  weight 
of  lead  or  iron  is  fastened  to  give  the  apparatus  when  floated 
on  water  a  greater  stability.  The  float  is  placed  on  the  sur- 
face of  the  water  in  a  pneumatic  trough  and  a  5  mm.  piece 
of  well-dried  phosphorus  laid  on  the  crucible  lid.  A  tubu- 
lated bell-jar,  with  a  rather  wide  mouth  to  permit  of  the 
insertion  of  a  candle  on  a  wire,  is 
^^^.^^^  tightly  corked  and  placed  immedi- 

^  ^  ately  above  the  float  (Fig.  78).    The 

phosphorus  is  ignited  by  touching 
with  a  hot  iron  wire,  and  the  bell- 
jar  immediately  lowered  until  its 
mouth  is  sealed  with  water.  The 
phosphorus  burns  rapidly,  and  the 


Fig  78  ^Q'^\>  generated   by  the   combustion 

causes  the  gas  in  the  bell-jar  to  ex- 
pand and  bubble  out  to  a  certain  extent  under  the  mouth  of 
the  bell-jar.  As  soon  as  the  phosphorus  goes  out,  however, 
the  water  will  rise  in  the  bell-jar,  indicating  a  marked  con- 
traction in  volume.  On  lowering  the  bell-jar  until  the  level 
of  the  liquids  inside  and  outside  is  the  same,  the  cork  may  be 
removed  and  a  burning  candle  on  the  end  of  a  wire  lowered 
into  the  residual  gas.     It  will  be  immediately  extinguished. 

Large  cork  ;  crucible  cover  ;  tubulated  bell-jar  ;  candle  on  wire  ;  P. 

5.  By  the  removal  of  oxygen  from  the  air  by  burning  hydro- 
gen. —  When  hydrogen  is  burned  in  air  water  is  formed,  the 
greater  portion  of  which  is  immediately  condensed.  Hydro- 
gen from  a  Kipp  generator  is  passed  through  a  glass  tube 
(Fig.  79)  so  bent  as  to  rise  under  a  tubulated  bell-jar  and 


NITROGEN 


183 


r-^ 


Fig.  79 


have  its  tip  at  least  5  cm.  above  the  level  of  the  water.  The 
glass  tube  is  provided  with  a  platinum  tip  consisting  of  a 
small  piece  of  foil  rolled  around  a  glass  rod  and  inserted 
in  the  end  of  the  glass  tube.  After 
lighting  the  hydrogen  flame,  which 
should  not  be  too  high,  the  tubu- 
lated bell-jar,  securely  corked  at 
the  tubulature,  is  lowered  over  the 
burning  jet.  The  oxygen  is  rapidly 
burned  to  form  water,  which  de- 
posits on  the  sides  of  the  jar  as  a 
mist.  As  it  is  somewhat  difficult 
to  observe  the  hydrogen  flame,  it  is 

best  to  moisten  the  tip  of  the  platinum  with  a  little  sodium 
chloride  solution  to  impart  a  color  to  the  flame.  The  instant 
the  flame  is  extinguished  the  supply  of  hydrogen  should  be 
cut  oif  and  the  burner  removed,  as  otherwise  the  admission 
of  unburned  hydrogen  will  contaminate  the  nitrogen.  The 
level  of  the  water  on  the  inside  of  the  bell-jar  will  have 
risen  considerably  and,  as  in  the  preceding  experiment,  the 
bell-jar  should  be  lowered  until  the  inner  and  outer  levels 
are  the  same  before  removing  the  stopper.  The  tubulature 
should  be  large  enough  to  permit  the  introduction  of  a  burn- 
ing candle  in  testing  the  gas.  It  is  of  the  utmost  impor- 
tance that  the  hydrogen  flame  should  be  watched  and  the 
supply  of  hydrogen  cut  off  the  moment  the  flame  is  ex- 
tinguished. This  separation  of  oxygen  and  nitrogen  is 
extremely  simple  and  not  difficult  of  comprehension  by  ele- 
mentary students,  as  oxygen,  hydrogen,  nitrogen,  and  water 
are  familiar  substances. 

Tubulated  bell-jar  ;  jet  with  Pt  tip  ;  H  supply  ;  NaCl  solution. 


6.  By  the  combustion  of  air  and  ammonia  on  copper. — When 
large  quantities  of  nitrogen  are  desired,  by  far  the  most  sat- 


184 


CHEMICAL  LECTURE   EXPERIMENTS 


isfactory  method  for  obtaining  it  is  that  in  which  a  mixture 
of  air  and  ammonia  gas  is  passed  over  a  hot  copper  coil, 
which  is  alternately  oxidized  by  the  air  and  reduced  by  the 
ammonia,  forming  water  and  nitrogen.  The  air  is  obtained 
from  an  ordinary  water-blast,  and  the  ammonia  vapor  from 
the  strongest  aqua  ammonia,  which  is  placed  in  a  gas  wash- 
ing-bottle (Fig.  80).  The  air  is  allowed  to  bubble  through 
the  liquid  and  become  saturated  with  the  ammonia  gas.  The 
gaseous  mixture  is  then  passed  into  a  30  cm.  length  of  com- 
bustion tubing  contain- 
ing a  coil  of  copper  wire 
and  fitted  with  a  deliv- 
[j:^  ery-tube  at  the  other  end 
leading  to  a  pneumatic 
trough  containing  acidu- 
lated water.  The  copper 
coil  is  heated  by  means  of 
a  strong  Bunsen  burner 
at  the  end  nearest  the 
entrance  of  the  gases.  The  copper  will  become  oxidized 
by  the  oxygen  of  the  air,  and  the  copper  oxide  thus  formed 
be  immediately  reduced  by  the  ammonia  gas,  forming  water 
and  nitrogen.  The  reduced  copper  is  then  immediately 
oxidized  and  reduced,  the  process  being  a  continuous 
one.  The  air,  deprived  of  its  oxygen  by  the  copper, 
passes  on  as  nitrogen  into  the  pneumatic  trough.  To  this 
nitrogen  is,  of  course,  added  the  nitrogen  liberated  from 
the  ammonia.  As  the  reaction  proceeds,  the  copper  coil 
becomes  intensely  hot  and  the  external  heat  may  be  with- 
drawn. There  should  always  be  an  excess  of  ammonia  gas 
in  the  air  current,  and  consequently  all  of  the  spiral  but 
the  front  end  should  be  in  the  reduced  state.  As  soon 
as  it  begins  to  oxidize  for  any  distance  it  is  an  indication 
that  the  supply  of  ammonia  is  becoming  exhausted.      By 


\7 


^ 


Fig.  80 


NITROGEN  185 

observing  the  color  of  the  spiral,  the  operation  can  be  well 
regulated.  The  excess  of  ammonia  vapor  carried  along  to 
the  pneumatic  trough  will  be  dissolved  in  the  water,  and 
unless  large  quantities  of  nitrogen  are  to  be  prepared  and 
the  water  becomes  saturated  with  the  ammonia,  no  precau- 
tion is  necessary.  It  may,  however,  be  necessary  after  a 
while  to  have  free  sulphuric  acid  present  to  neutralize  the 
ammonia  as  it  is  dissolved.  When  very  strong  ammonia 
water  is  used  in  the  gas  washing-bottle,  it  is  found  that  a 
good  strong  air-blast  is  necessary. 

2  NH3  4-  3  CuO  =  3  H2O  -f  3  Cu  -f  N2. 

Air-blast ;  gas  washing-bottle ;  combustion-tube  ;  strongest  NH4OH  ; 
Cu  coil. 

7.  Oxidation  of  nitrogen  by  burning  magnesium  in  air.  — 

The  heat  of  burning  magnesium  is  sufficient  to  cause  a 
union  of  nitrogen  and  oxygen  in  small  quantities. 

An  8  cm.  piece  of  magnesium  ribbon  is  tied  to  a  stout 
iron  wire  and  after  ignition  quickly  lowered  into  a  clean,  dry 
500  cc.  cylinder  having  a  layer  of  sand  on  the  bottom.  The 
nitrogen  and  the  oxygen  of  the  air  are  caused  to  combine,  and 
a  strong  test  for  nitrous  acid  is  obtained  with  iodo-starch 
paper  lowered  into  the  cylinder.  The  layer  of  sand  pre- 
vents the  cylinder  from  cracking  if  bits  of  burning  magne- 
sium fall  to  the  bottom. 

500  cc.  cylinder ;  Mg  ribbon  ;  Kl-starch  paper, 

8.  Formation  of  oxides  of  nitrogen  by  the  combustion  of 
hydrogen  in  oxygen.  —  The  union  of  nitrogen  and  oxygen 
may  be  brought  about  by  the  intense  heat  of  the  hydrogen 
flame  burning  in  oxygen  mixed  with  a  small  quantity  of  air. 
A  clean,  dry  Erlenmeyer  flask  of  1  or  2  1.  capacity  is  filled 
with  oxygen  by  displacement  and  a  burning  jet  of  hydrogen 
lowered  into  the  flask.     On  account  of  the  heat  generated  it 


186  CHEMICAL   LECTURE   EXPERIMENTS 

is  necessary  to  have  a  platinum  tip  on  the  glass  tube  as  is 
recommended  in  Ex.  5.  The  mouth  of  the  flask  being 
open,  a  certain  amount  of  air  can  enter,  and  a  portion  of 
its  nitrogen  will  combine  with  the  oxygen  to  form  nitrous 
acid.  After  allowing  the  hydrogen  to  burn  for  a  few  minutes 
the  jet  is  withdrawn  and  moistened  iodo-starch  paper  is 
held  in  the  flask.  It  is  immediately  colored  blue,  indicat- 
ing the  presence  of  nitrous  acid. 

Jet  (Fig.  41,  p.  85)  ;  H  generator;  jar  of  0  ;  Kl-starch  paper. 


ATMOSPHERIC   AIR 

9.  Determination  of  oxygen  in  air  by  potassium  pyrogal- 
late.  —  One  hundred  cubic  centimeters  of  air  are  introduced 
into  the  eudiometer  (Fig.  11,  p.  26),  and  potassium  pyrogallate 
solution  (Ex.  21,  p.  26)  allowed  to  flow  slowly  down  through 
the  gas.  The  absorption  will  have  ceased  when  the  liquid 
stops  rising  in  the  tube.  Before  reading  off  the  volume  of 
the  remaining  gas  the  reagent  should  be  washed  out  of  the 
tube  by  allowing  successive  portions  of  water  to  flow  through 
the  stop-cock.  It  will  be  found  that  the  volume  has  dimin- 
ished 20  cc,  or  one-fifth. 

The  method  is  capable  of  yielding  very  accurate  analyses 
if  the  eudiometer  is  lowered  in  taking  each  reading  till  the 
levels  of  the  inner  and  outer  liquids  are  the  same.  In  exact 
measurements,  however,  fluctuations  in  the  temperature  of 
the  gas  must  be  avoided. 

Eudiometer,  Fig.  11,  p.  26  ;  potassium  pyrogallate  solution. 

10.  Quantitative  determination  of  nitrogen  in  air.  —  While 
the  combination  of  burning  phosphorus  and  oxygen  attended 
by  light  and  heat  is  extremely  rapid,  the  elements  do,  never- 
theless, unite  at  ordinary  temperatures. 


ATMOSPHERIC    AIR 


187 


r\ 


One  hundred  cubic  centimeters  of  air  are  introduced  into 
a  eudiometer  tube.  A  stick  of  phosphorus  3  or  4  cm.  long 
is  carefully  cleaned  under  water  and  fastened  to  a  piece  of 
copper  wire.  The  phosphorus  is  then  thrust  under  the 
mouth  of  the  eudiometer  tube,  which 
remains  under  water  and  is  pushed  a 
considerable  distance  up  the  tube,  into 
the  air.  The  copper  wire  is  then  bent 
so  as  to  rest  on  the  bottom  of  the  dish 
and  support  the  phosphorus  in  the  air 
(Fig.  81).  The  level  of  the  water  in  the 
tube  will,  of  course,  be  depressed  by  as 
much  as  the  volume  of  the  copper  and 
the  phosphorus  introduced.  Hence  it  is 
important  that  the  eudiometer  be  of  suffi- 
cient size  to  allow  of  this  expansion  over 
the  100  cc.  After  the  whole  apparatus 
has  stood  over  night  it  will  be  found 
that  a  diminution  in  volume  has  taken 
place.  By  withdrawing  the  phosphorus  and  reading  off  the 
volume  of  the  residual  gas  it  will  be  found  to  be  approxi- 
mately 80  cc,  i.e.,  four-fifths  of  the  original  volume. 

In  case  a  graduated  tube  is  not  at  hand  a  linear  measure- 
ment of  the  diminution  may  be  made. 

Eudiometer  tube  2  cm.  in  diameter  ;   meter  stick  ;  P  ;  Cu  wire. 


11.  Quantitative  absorption  of  oxygen  from  air  by  metallic 
copper.  —  By  measuring  the  quantity  of  air  passed  over  a 
heated  copper  coil  and  the  amount  of  gas  collected  at  the 
pneumatic  trough,  the  proportion  of  oxygen  and  nitrogen 
present  in  the  air  may  be  quantitatively  determined. 

A  stoppered  cylinder  is  fitted  with  a  two-holed  rubber  stop- 
per carrying  one  tube  leading  to  the  bottom  of  the  cylinder 
and  a  glass  elbow  directly  connected  with  the  combustion-tube 


188 


CHEMICAL  LECTURE  EXPERIMENTS 


containing  the  copper  coil.  Connection  is  then  made  with  a 
faucet,  so  that  by  opening  the  valve,  water  may  be  allowed  to 
flow  into  the  glass  cylinder,  expelling  the  air  at  the  top 
through  the  elbow  into  the  combustion-tube.  After  making 
all  the  connections  the  combustion-tube  containing  the  cop- 
per is  brought  to  red  heat,  the  expanded  air  being  allowed  to 
escape  at  the  pneumatic  trough  (Fig.  82).  When  a  constant 
temperature  has  been  reached,  noted  by  the  absence  of  air 
bubbles  from  the  delivery-tube,  an  inverted  graduated  stop- 
pered liter  cylinder  filled  with  water  is   placed   over   the 


Fig,  82 


delivery-tube  and  water  allowed  to  flow  slowly  into  the 
first  graduate.  The  rate  must  not  be  too  rapid,  as  otherwise 
the  absorption  of  oxygen  would  not  be  complete.  Water  is 
allowed  to  flow  into  the  first  cylinder  until  it  has  reached 
the  1000  cc.  graduation.  The  volume  of  gas  collected  at  the 
pneumatic  trough  will  be  found  to  be  about  800  cc.  More 
exact  measurement  may  be  made  by  lowering  the  graduate 
into  a  deep  vessel  until  the  inner  and  outer  levels  of  the 
water  are  the  same.  It  is  thus  seen  that  from  1000  cc.  of 
air,  approximately   800   cc.  of   nitrogen  remain  after   the 


AMMONIA  189 

absorption  of  200  cc.  of  oxygen.  Both  cylinders  should  be 
protected  from  any  undue  heating  by  asbestos  sci'eens  placed 
between  them  and  the  burner. 

Two  1000  cc.  graduated  stoppered  cylinders ;  combustion-tube ; 
Cu  coil. 

12.  Quantitative  combustion  of  phosphorus  in  a  confined 
volume  of  air.  —  The  regularity  of  the  combustion  of  red 
phosphorus  in  air  makes  this  form  of  phosphorus  better 
adapted  for  the  experiment  in  which  oxygen  is  burned  out  of 
a  confined  volume  of  air. 

A  crucible  lid  containing  red  phosphorus  is  arranged 
as  in  Ex.  4,  and  a  tubulated  bell-jar  placed  over  the  float. 
A  mark  on  the  bell-jar  is  made  about  2  cm.  from  the  mouth 
and  the  remaining  volume  divided  into  fifths.  The  red 
phosphorus  in  the  crucible  lid  is  provided  with  a  small  piece 
of  touch-paper,  which  is  ignited.  The  bell-jar  with  the  cork 
removed  is  lowered  into  water  to  the  point  marked  2  cm. 
above  the  mouth.  The  cork  is  then  inserted,  and  when  the 
phosphorus  itself  begins  to  burn  the  water  in  the  bell-jar 
rises  as  the  oxygen  is  consumed.  The  contraction  of  the 
gas  (one-fifth  of  the  original  volume)  is  very  accurately 
noted  by  means  of  this  apparatus.  The  pneumatic  trough 
should  be  deep  enough  to  lower  the  jar  at  the  end  of  the 
experiment  till  the  inner  and  outer  levels  are  the  same. 

Tubulated  bell-jar  (graduated  in  fifths)  ;  crucible  lid  on  cork  ;  red  P  ; 
touch-paper. 

AMMONIA 

FORMATION   AND    PREPARATION 

13.  By  the  ignition  of  organic  substances.  —  (a)  A  small 
quantity  of  gelatine  or  glue  heated  in  a  test-tube  yields 
ammonia. 

Gelatine  or  dry  glue. 


190  CHEMICAL  LECTURE   EXPERIMENTS 

(b)  The  presence  of  ammonia  may  be  established  in  the 
products  of  the  dry  distillation  of  coal  (Ex.  62,  p.  325)  by 
inserting  a  piece  of  moistened  red  litmus  paper  in  the  filter- 
flask  of  the  apparatus  (Fig.  130,  p.  325). 

14.  By  heating  organic  nitrogenous  matter  with  soda- 
lime.  —  While  gelatine  and  similar  compounds  give  nitrogen 
directly  on  ignition,  many  organic  substances  containing 
nitrogen  —  uric  acid,  for  example —  do  not  yield  ammonia 
by  simple  heating. 

A  small  quantity  of  uric  acid  heated  in  a  test-tube  gives 
no  test  for  ammonia. 

When  such  compounds  are  intimately  mixed  with  dry 
sodarlime  and  ignited,  their  nitrogen  is  converted  into  am- 
monia. If  uric  acid  is  heated  with  an  equal  volume  of  fused 
dry  soda-lime  in  a  hard-glass  test-tube,  ammonia  is  evolved. 

Uric  acid  ;  dry  soda  lime. 

15.  By  heating  potassium  nitrate,  potassium  hydroxide,  and 
iron  powder.  —  When  iron  powder  is  heated  in  the  presence 
of  potassium  hydroxide,  hydrogen  is  liberated  in  a  manner 
similar  to  that  shown  in  Ex.  5,  p.  42.  As  is  seen,  however, 
in  Ex.  3,  the  ignition  of  iron  and  potassium  nitrate  yields 
nitrogen.  Heating  equal  volumes  .5  g.  each  of  potassium 
hydroxide  and  potassium  nitrate  with  20  g.  of  iron  fillings 
in  a  hard-glass  test-tube  gives  a  copious  evolution  of 
ammonia. 

Fe  powder  ;  KNOs  ;  KOH. 

16.  From  hydrogen  and  nitric  oxide. —  If  a  mixture  of 
hydrogen  and  nitric  oxide  is  passed  over  heated  platinized 
asbestos  5  volumes  of  the  hydrogen  combine  with  2  vol- 
umes of  the  nitric  oxide  and  ammonia  is  formed. 

Hydrogen  from  a  Kipp  generator  is  passed  through  a  glass 


AMMONIA  191 

tube  thrust  through  a  three-holed  cork  in  the  neck  of  a  small 
bottle  containing  a  2  cm.  layer  of  sulphuric  acid.  A  stream 
of  nitric  oxide  (Ex.  49,  p.  211)  passes  through  a  second  glass 
tube  into  the  bottle.  Both  tubes  dip  beneath  the  surface  of 
the  sulphuric  acid  that  their  rate  of  bubbling  may  be  noticed. 
Hydrogen  is  conducted   through 


the  whole  apparatus  to  drive  out   ^ ^11  ^^      S)' 

all  air  and  then  the  nitric  oxide  ^  ^ 


generator  started.  The  current  of 
hydrogen  should  be  three  times 
as  fast  as  the  current  of  nitric 
oxide.  The  mixed  gases  are  then  — -—  ^^^^  ^^ 
conducted  through  a  piece  of  com- 
bustion-tubing or  a  bulb-tube  containing  platinized  asbestos 
(Fig.  83).  Until  the  asbestos  is  heated  no  ammonia  is 
present  in  the  issuing  gases,  which  redden  on  exposure  to 
the  air ;  but  on  heating  the  asbestos  a  strong  test  for  am- 
monia is  immediately  obtained  and  no  red  fumes  are  formed. 

2  NO  -1-  5  Ha  =  2  NH3  -f-  2  H2O. 

H  generator  ;  NO  generator ;  wash-bottle,  with  3-holed  cork  ;  bulb- 
tube  ;  platinized  asbestos. 

17.   From  ammoniiiin  hydroxide  and  potassium  hydroxide. 

Strong  ammonium  hydroxide  is  allowed  to  drop  from  a  sep- 
arating-f unnel  upon  solid  potassium  hydroxide,  preferably  in 
the  stick  form,  in  a  500  cc.  Erlenmeyer  jflask  (Fig.  3,  p.  11). 
The  dropping-funnel  is  placed  in  a  two-holed  rubber  stopper, 
and  a  glass  elbow  conducts  away  the  gaseous  ammonia  liber- 
ated. In  the  process  of  the  reaction  the  contents  of  the 
flask  become  very  cold  from  the  volatilization  of  ammonia, 
and  consequently  the  gas  is  quite  dry.  However,  in  all 
experiments  where  a  perfectly  dry  gas  is  required  it  should 
be  first  conducted  through  a  U-tube  containing  dry  quick- 


192  CHEMICAL   LECTURE   EXPERIMENTS 

lime  or  soda-lime.  This  method  is  by  far  the  most  conven- 
ient and  available  one  for  obtaining  varying  quantities  of 
ammonia  on  the  lecture  table. 

Apparatus,  Fig.  3,  p.  11  ;  500  cc.  flask  ;  dropping-funnel ;  stick 
KOH  ;  con.  NH4OH. 

18.  By  heating  ammonium  hydroxide.  —  One  of  the  most 
convenient  sources  of  gaseous  ammonia  is  the  strongest  aqua 
ammonia  of  commerce.  The  simple  application  of  heat 
suffices  to  drive  off  the  ammonia  which,  when  dried,  is 
ready  for  use.  The  aqueous  ammonia  is  placed  in  a  flask 
fitted  with  a  thistle-tube  and  a  glass  elbow.  On  gently 
warming,  ammonia  is  driven  off  and  passes  through  a  gas 
washing-bottle  containing  a  small  quantity  of  strongest 
ammonia  water,  and  then  through  a  U-tube  containing  quick- 
lime or  fused  soda-lime  to  dry  the  gas,  which  may  be  col- 
lected over  mercury.  The  gas  washing-bottle  with  the 
strong  ammonia  water  is  used  to  show  by  the  bubbling  the 
rate  at  which  the  gas  is  given  off.  Calcium  chloride  cannot 
be  used  to  dry  ammonia,  as  it  forms  a  compound  with  the 
gas,  and  hence  quicklime  or  soda-lime  is  recommended. 
The  gas  may  be  collected  over  mercury  or  by  displacement. 

Flask  with  thistle-tube  and  elbow  ;  gas  washing-bottle  ;  U-tube  with 
soda-lime ;  strongest  NH4OH. 

19.  From  ammonium  chloride  and  slaked  lime. —  Powdered 
ammonium  chloride  and  slaked  lime  in  equal  quantities 
(about  40  g.  of  each)  are  placed  in  a  300  cc.  Jena  glass 
Erlenmeyer  flask  fitted  with  a  safety-tube  (such  as  is  shown 
in  Fig.  85,  p.  196)  and  a  glass  elbow.  A  small  quantity  of 
concentrated  ammonium  hydroxide  or  mercury  is  placed  in 
the  bend  of  the  safety-tube.  On  the  application  of  gentle 
heat  ammonia  is  rapidly  evolved.  The  gas  may  be  dried  by 
conducting  it  through   a  U-tube   containing   quicklime  or 


AMMONIA  193 

fused  soda-lime.  Owing  to  its  low  specific  gravity,  ammonia 
can  be  readily  collected  by  displacement  of  air  according  to 
the  method  of  collecting  hydrogen.  Almost  invariably  this 
method  of  collecting  the  gas  may  be  used. 

2  NH4CI  +  Ca(0H)2  =  CaCla  +  2  H^O  +  2  NH3. 

300  cc.  Jena  glass  Erienmeyer  flask  ;  safety-tube  ;  soda-lime  drying- 
tube  ;  NH4CI ;  Ca(0H)2. 

PROPERTIES 

20.  Specific  gravity.  —  Ammonia  is  considerably  lighter 
than  air,  resembling  hydrogen  in  this  respect. 

A  jar  of  ammonia  may  be  opened  under  the  mouth  of  an 
inverted  beaker  suspended  on  the  end  of  a  balance  which 
has  been  brought  into  equilibrium.  On  allowing  the  ammo- 
nia to  rise  into  the  beaker  and  expel  the  air  the  equilibrium 
will  be  disturbed. 

Lecture-balance  ;  inverted  beaker  ;  jar  of  NH3. 

21.  Alkaline  nature  and  tests. — (a)  Ammonia  gas  imparts 
the  color  characteristic  of  alkalies  to  papers  saturated  with 
solutions  of  litmus,  cochineal,  turmeric,  or  phenol-phthalein. 
The  papers  may  be  held  in  a  jar  of  ammonia  or  at  the 
mouth  of  a  bottle  containing  strong  ammonium  hydroxide. 

Ammonia,  however,  is  a  volatile,  as  distinguished  from  a 
fixed,  alkali,  and  if  the  papers  colored  by  ammonia  are 
allowed  to  remain  in  the  air,  the  original  colors,  or  in  case  of 
phenol-phthalein  absence  of  color,  will  return. 

Litmus,  turmeric,  cochineal,  phenol-phthalein  papers,  or  solutions  of 
these  indicators  ;  strong  NH4OH  ;  dry  red  litmus  paper. 

(b)  With  gaseous  hydrogen  chloride.  —  If  a  rod  moistened 
with  concentrated  hydrochloric  acid  is  held  at  the  mouth  of 
a  test-tube  from  which  ammonia  is  escaping,  white  fumes  of 
ammonium  chloride  will  be  formed. 


194  CHEMICAL   LECTURE   EXPERIMENTS 

(c)  Action  on  mercurous  nitrate.  —  A  piece  of  filter-paper 
dipped  in  mercurous  nitrate  solution  is  instantly  turned 
black  in  the  presence  of  ammonia. 

Hg2(N08)2  solution. 

22.  Solubility  in  water.  —  A  tall  glass  cylinder  is  filled 
with  ammonia  by  displacement,  covered  with  a  metal  disk, 
and  opened  under  water  by  slowly  sliding  the  disk  to  one 
side.  The  water  rushes  up  into  the  cylinder  with  almost 
explosive  violence.  On  account  of  this  rapid  solubility  of 
the  gas  in  water  the  use  of  a  metal,  rather  than  a  glass,  cover 
is  recommended,  as  the  latter  might  be  broken  by  the  rapid 
inrush  of  water. 

Cylinder  of  NH3  ;  metal  disk. 

23.  Solubility  in  water  producing  a  fountain.  —  A  2  1. 

round-bottomed  flask  is  filled  with  ammonia  by  displace- 
ment, the  gas  entering  through  a  long  tube  pushed  through 
a  two-holed  rubber  stopper  leading  to  the  bottom  of  the 
flask,  which  is  supported  in  an  inverted  position.  When 
completely  filled  with  ammonia,  the  cork  and  the  tube  are  rap- 
idly withdrawn  and  another  two-holed  rubber  stopper,  with 
fittings  described  beyond,  is  rapidly  inserted  in  the  neck  of 
the  flask.  Through  one  of  the  holes  in  the  cork  a  long  glass 
tube,  whose  end  has  been  drawn  out  to  a  2  mm.  opening,  is 
thrust  until  the  jet  is  about  in  the  centre  of  the  flask  (Fig. 
84).  The  other  end  of  the  tube,  which  must  extend  some 
25  or  30  cm.  beyond  the  cork,  is  plugged  with  a  small  piece 
of  rubber  tubing  and  a  bit  of  glass  rod,  and  dips  into  a  crys- 
tallizing dish  filled  with  a  slightly  acid  solution  of  litmus. 
Through  the  other  hole  of  the  cork  is  thrust  an  ordinary 
medicine  dropper  which  has  been  filled  with  water  to  within 
a  few  millimeters  of  the  end  of  the  jet.  It  is  important  to 
have  the  rubber  bulb  as  well  as  the  glass  portion  of  the  dropper 


AMMONIA 


195 


filled  with  water.  The  whole  apparatus  is  firmly  supported 
on  the  ring  of  a  retort  stand.  On  removing  the  plug  from 
the  end  of  the  tube  dipping  under 
water  no  action  takes  place,  as  there 
is  a  long  layer  of  air  in  the  tube  be- 
tween the  ammonia  and  water.  On 
pinching  the  bulb  of  the  dropper  a 
few  cubic  centimeters  of  water  are 
suddenly  introduced  into  the  flask, 
and  absorption  is  instantaneous,  the 
vacuum  produced  being  sufficient  to 
cause  the  water  to  ascend  the  long 
tube  and  play  out  of  the  jet  as  a 
fountain.  The  alkalinity  of  the  water 
is  strikingly  shown  by  the  change  in 
color  of  the  litmus  solution. 

In  case  the  flask  has  been  com- 
pletely filled  with  gaseous  ammonia, 
water  will  rush  in  till  the  flask  is 
full.  Provision  must  be  made  for  the 
addition  of  water  to  the  crystallizing 

dish  as  fast  as  it  is  withdrawn.*    The  support  must  be  strong 
enough  to  hold  up  the  flask  when  filled  with  2  1.  of  water. 

2  1.  flask  (dry)  ;   2-holed  cork  and   jet ;    medicine  dropper ;  NHj 
generator  ;  soda-lime  drying-tube  ;  litmus  solution. 


Fig.  84 


24.   Collection  over  mercury  and  absorption  by  water.  — 

Gaseous  ammonia,  owing  to  its  great  solubility  in  water,  can 
be  collected  only  over  mercury.  Dried  gaseous  ammonia 
is  collected  in  a  thick-walled  test-tube  over  mercury,  care 
being  taken  not  to  have  the  delivery-tube  dip  too  deeply 
into  the  mercury,  thereby  increasing  the  pressure  to  be  over- 
come. The  great  solubility  of  ammonia  is  seen  when  a  few 
drops  of  water  are  allowed  to  enter  the  tube  through  a 


196 


CHEMICAL   LECTURE   EXPERIMENTS 


hooked  glass  tube  and  to  rise  through  the  mercury  and 
come  in  contact  with  the  gaseous  ammonia.  The  absorption 
is  very  rapid,  the  mercury  rising  in  the  tube  to  take  the 
place  of  the  absorbed  gas. 

A  piece  of  ice  may  be  used  instead  of  water. 

Mercury  trough  ;  NH3  supply  ;  ice. 

25.   Preparation    of     ammonium    hydroxide     (ammonia 

water).  —  Ammonium  hydroxide  is  prepared  by  saturating 
water  with  gaseous  ammonia. 

Ammonia  gas  is  generated  as  in  Ex.  19,  and  conducted 
directly  from  the  flask  without  the  introduction  of  a  drying- 
tube  into  an  empty  gas  washing-bottle  which  serves  to  col- 
lect any  solid  particles  m'echanically  carried  over.^ 


Fig.  85 

The  gas  is  then  conducted  through  a  series  of  three  3- 
necked  Wolff  bottles  of  300-400  cc.  capacity,  each  half  filled 
with  distilled  water  (Fig.  85).  Each  Wolff  bottle  is  fitted 
with  an  elbow  reaching  to  the  bottom  of  the  bottle,  a  verti- 
cal safety -tube  dipping  just  beneath  the  surface  of  the  water, 
and  an  elbow  extending  just  below  the  cork.  As  soon  as  all 
the  air  is  driven  out  of  the  generating  flask,  the  bubbles 

1  When  a  large  quantity  of  ammonia  is  desired,  100  g.  each  of 
ammonium  chloride  and  calcium  hydroxide  should  be  heated  in  a 
500  cc.  flask. 


AMMONIA  197 

rising  through  the  water  in  the  first  of  the  series  of  Wolff 
bottles  grow  smaller,  and  finally  all  the  gas  is  absorbed.  As 
soon  as  the  water  in  this  bottle  becomes  nearly  saturated 
the  gas  rises  through  the  solution  unabsorbed  and  passes 
through  the  elbow  into  the  second  bottle,  etc. 

As  the  ammonium  hydroxide  is  lighter  than  water,  it  is 
important  that  the  glass  elbows  extend  to  the  bottom  of 
each  bottle,  as  otherwise  the  upper  surface  of  the  liquid 
would  become  saturated,  while  the  lower  strata  would  be  but 
slightly  alkaline. 

NHg     +     H2O    =    NH4OH. 

Apparatus  (Fig.  85)  ;  500  cc.  Jena  glass  Erlenmeyer  flask ;  three 
3-necked  Wolff  bottles  ;  NH^Cl ;  Ca(0H)2. 

26.  Absorption  by  charcoal. — Freshly  ignited  charcoal 
absorbs  large  quantities  of  ammonia. 

Ammonia  collected  over  mercury  as  in  Ex.  24,  is  rapidly 
absorbed  by  a  centimeter  piece  of  heated  charcoal  imme- 
diately introduced  under  the  mercury  so  as  to  come  in  con- 
tact with  the  gas.  As  the  gas  is  absorbed,  the  mercury  rises 
rapidly  to  take  its  place. 

Tube  filled  with  NH3  over  mercury  ;  charcoal. 

27.  Absorption  by  fused  calcium  chloride. — Fused  cal- 
cium chloride  absorbs  ammonia,  forming  a  definite  chemical 
compound.  For  this  reason  calcium  chloride,  so  often  used 
as  a  dryer  for  gases,  cannot  be  used  for  drying  ammonia. 
Ignited  soda-lime  or  quicklime  is  usually  used  for  this 
purpose. 

A  small  piece  of  fused  calcium  chloride  is  slipped  under 
a  tube  filled  with  gaseous  ammonia  over  mercury  (Ex,  24). 
Immediately  the  absorption  begins,  and  the  calcium  chloride 
melts. 

Tube  filled  with  NHg  over  mercury  ;  fused  CaCla- 


198  CHEMICAL  LECTURE   EXPERIMENTS 

28.  Absorption  by  silver  chloride.  —  Silver  chloride,  as 
well  as  calcium  chloride,  absorbs  ammonia,  forming  a  defi- 
nite compound.  A  few  fragments  of  precipitated  silver 
chloride  (residues  from  chlorine  determinations)  are  slipped 
under  a  test-tube  of  ammonia  collected  over  mercury.  The 
ammonia  is  rapidly  absorbed,  mercury  rising  to  take  its 
place. 

On  heating  the  silver  compound  ammonia  is  again  ex- 
pelled. 

Tube  filled  with  NHg  over  mercury  ;  AgCl. 

29.  Combustion  in  air.  —  (a)  Ammonia,  owing  to  its  large 
percentage  of  hydrogen,  is  somewhat  combustible  in  air, 
though  only  noticeably  so  under  certain  conditions. 

The  flame  of  a  Bun  sen  burner  is  turned  very  low,  and 
gaseous  ammonia  is  conducted  through  a  drawn-out  glass  jet 
bent  at  the  end  so  as  to  deliver  the  gas  into  the  centre  of 
the  burner.  The  glass  jet  is  introduced  upward  into  one  of 
the  air-holes.  The  ammonia  will  burn  with  a  characteristic 
yellowish  flame. 

A  very  interesting  study  of  the  structure  of  the  flame  may 
be  made  by  allowing  a  gentle  stream  of  ammonia  to  enter 
the  air-holes  in  the  bottom  of  a  Bunsen  burner.  The  burner 
should  give  a  good  flame  and  be  turned  on  full.  The  am- 
monia will  impart  a  yellowish  cast  to  the  whole  flame 
and  the  outlines  of  the  several  cones  will  be  distinctly 
seen. 

When  a  Bunsen  burner  is  held  at  the  mouth  of  a  tube  at 
which  ammonia  gas  is  escaping,  the  flame  is  colored  yellow, 
and  on  close  inspection  it  will  be  observed  that  particularly 
when  the  end  of  the  tube  becomes  hot  there  is  a  distinct 
combustion  of  the  ammonia  itself. 

NHg  supply. 


AMMONIA  199 


lib 


(6)   Ammonia  gas  issuing  from  a  glass  jet  will  not  con- 
tinue to  burn  in  air,  as  the  temperature  of  its 
own  flame  is  not  sufficiently  high  to  dissociate  (Irf^ 

the  ammonia  gas.    The  necessary  heat  is  easily  ^^\'  ' 

furnished  by  passing  the  gas  through  the  ring 
of  flame  at  the  mouth  of  a  central  draft  burner. 

The  flame  of  an  Erlenmeyer  burner  is  turned 

as  low  as  possible  and  yet  leave  a  small  ring 

of  blue  flame  around  the  central  draft  tube  '-i)^ 

(Fig.  86).      In  the  base  of  this  tube  a  cork 

•  1  11  .      .  -,         »  .  Fig.  86 

carrying  a  glass  elbow  is  inserted.     Ammonia 

gas  is  led  through  the  glass  elbow  and  burns  at  the  top 

with  a  yellowish  flame. 

Erlenmeyer  burner  ;  NH3  supply. 

30.  Combustion  in  oxygen.  —  A  gentle  stream  of  ammonia, 
generated  by  warming  20  cc.  of  the  concentrated  liquid  in  a 

50  cc.  Erlenmeyer  flask,  is  made  to  enter  an 

open  tube  filled  with  oxygen.     The  glass  tube 

conducting  the  ammonia  is  passed  through  a 

two-holed  rubber  stopper  fitted  into  the  end 

of  a  short  piece  of  wide  glass  tubing  (Fig.  87). 

A  gentle  stream  of  oxygen  is  allowed  to  enter 

IJ  y         through  a  glass  elbow  and  maintain  an  atmos- 

^t^        phere  of  oxygen  about  the  open  tube  leading 

Fig.  87         from  the  ammonia  flask.    The  ammonia  burns 

with  a  distinctly  luminous  flame. 
Apparatus  (Fig.  87)  ;  con.  NH4OH ;  O  supply. 

31.  Combustion  of  oxygen  in  ammonia.  —  A 150  cc.  beaker 
is  half  filled  with  the  strongest  ammonium  hydroxide  and 
very  gently  warmed.  A  slow  current  of  oxygen  is  passed 
through  a  long  tube  3  or  4  mm.  in  diameter  whose  end 
almost  touches  the  surface  of  the  liquid.     A  flame  is  then 


200  CHEMICAL   LECTURE    EXPElllMENTS 

brought  to  the  mouth  of  the  beaker,  and  soon  the  oxygen  is 

seen  burning  at  the  end  of  the  tube.  The  tube  is  then 
quickly  immersed  in  the  liquid  and  the 
current  of  oxygen  simultaneously  in- 
creased (Fig.  88).  A  green  flame  of 
considerable  size  appears  in  the  beaker, 
and  the  oxygen  is  seen  to  be  burning 
beneath  the  surface  of  the  liquid.  In 
a  very  few  moments  the  ammonium  hy- 
droxide will  have  lost  so  much  of  the 

dissolved  ammonia  as  to  be  too  dilute  for  the  continuation 

of  the  experiment. 

Strongest  NH4OH  ;  0  supply. 

32.  Decomposition  by  metallic  potassium.  —  Potassium 
unites  with  ammonia,  setting  free  some  of  the  hydrogen. 

A  7  mm.  piece  of  potassium  is  placed  in  a  hard-glass  bulb- 
tube  and  a  gentle  current  of  dry  ammonia  passed  through 
it.  On  heating  the  bulb  the  potassium  melts,  and  if  heated 
strongly,  the  molten  globule  suddenly  bursts,  filling  the  bulb 
with  the  characteristic  green  vapor  of  potassium.  The  hydro- 
gen set  free  may  be  ignited  at  the  open  end  of  the  bulb-tube. 

Bulb-tube  ;  K  ;  NH3  supply. 

33.  Decomposition  of  ammonia  by  platinized  asbestos. — 

When  dry  ammonia  is  passed  over  heated  platinized  asbestos 
in  a  combustion-tube,  the  gas  is  dissociated  and  three  volumes 
of  hydrogen  and  one  of  nitrogen  are  set  free.  The  gases  so 
liberated  may  be  collected  over  water  in  the  pneumatic 
trough  and,  owing  to  the  large  percentage  of  hydrogen,  may 
be  ignited.     ^ 

Ammonia  dried  by  passing  through  a  U-tube  filled  with 
soda-lime  or  quicklime  is  conducted  through  a  25  cm.  length 
of  combustion  tubing  fitted  with  a  cork  and  a  delivery-tube 


AMMONIA  201 

leading  to  the  pneumatic  trough.  A  5  cm.  length  of  platin- 
ized asbestos  is  placed  in  the  middle  of  the  combustion-tube 
and  brought  to  a  low  red  heat  by  means  of  a  Bunsen  burner. 
On  conducting  the  dry  ammonia  through  the  tube  all  the  gas 
will  be  absorbed  in  the  pneumatic  trough  as  soon  as  air  has 
been  driven  out  of  the  apparatus;  but  as  the  platinized 
asbestos  begins  to  be  heated,  small  quantities  of  gas,  rapidly 
increasing  with  the  increased  temperature,  will  be  collected 
at  the  pneumatic  trough.     On  applying  a  match  the  gas  will 

b^i'^-  2  NHg  =  Ng  +  3  H2. 

25  cm.  length  combustion  tubing ;  U-tube  containing  soda-lime  or 
quicklime  ;  platinized  asbestos  ;  NH3  supply. 

34.  Electrolysis  of  ammonium  hydroxide.  —  Ammonia  is 
decomposed  into  the  elements  hydrogen  and  nitrogen  when 
subjected  to  electrolysis. 

Strong  ammonium  hydroxide,  to  which  some  sodium  chlo- 
ride has  been  added  to  give  conductivity  to  the  solution,  is 
poured  into  the  electrolytic  apparatus  (Fig.  46,  p.  95)  and 
decomposed  by  means   of   a   current  of  from  four  to  six 
cells.      Platinum    electrodes    must   be    used.      In    a    short 
time  gas  will  be  collected  at  both  arms  of  the 
tube  in  the  proportion  of  three  volumes  in  one 
arm  to  one  volume  in  the  other.     The  larger 
volume  of  gas  can  be  tested  and  shown  to  be 
hydrogen,  by  opening  the  gas-cock  and  applying 
a  match.     The  sodium  chloride  in  the  solution 
will,  however,  impart  a  yellowish  color  to  the       "fiq,  gg 
flame.    The  smaller  volume  of  gas  can  be  trans- 
ferred to  a  test-tube  in  the  manner  shown  in  Fig.  89,  and 
proved  to  be  nitrogen  by  extinguishing  a  match. 

2NH3=:N2  +  3H2. 
Electrolytic    apparatus    (Fig.   46,   p.  95)  ;  battery  6  cells ;    con. 
NH4OH;  NaCl. 


202  CHEMICAL   LECTURE   EXPERIMENTS 

36.   Quantitative  decomposition  of  ammonia  by  chlorine. 

—  Chlorine  acts  on  ammoniiim  hydroxide  with  the  forma- 
tion of  hydrochloric  acid  and  the  liberation  of  nitrogen. 
Chlorine  abstracts  the  hydrogen  from  ammonia,  and  conse- 
quently for  every  three  volumes  of  chlorine  used  one  volume 
of  nitrogen  is  liberated. 

The  eudiometer  (Fig.  11,  p.  26)  is  filled  over  a  salt  solu- 
tion with  a  rapid  stream  of  pure  chlorine.  When  the  tube 
is  completely  filled,  a  well-fitting  rubber  stopper  is  crowded 
into  the  open  end  of  the  tube  while  still  under  the  salt 
solution,  care  being  taken  to  enclose  no  liquid  in  the  tube. 
A  few  cubic  centimeters  of  strongest  ammonium  hydroxide 
are  then  allowed  to  flow  through  the  funnel  into  the  gas, 
though  the  stop-cock  must  be  but  slightly  turned.  As  the 
ammonia  comes.in  contact  with  the  chlorine,  the  reaction  is 
very  vigorous  and,  owing  to  the  condensation  in  gas  volume,  a 
partial  vacuum  is  produced  inside  the  tube.  The  ammonium 
hydroxide  in  the  bulb  of  the  eudiometer  is  replaced  by 
water  acidulated  with  sulphuric  acid,  successive  portions 
poured  into  the  funnel  and,  by  opening  the  stop-cock, 
allowed  to  flow  into  the  eudiometer  till  the  internal  and  the 
external  pressure  are  the  same,  and  no  liquid  will  enter. 
The  volume  of  colorless,  residual  gas  will  be  found  to  be 
one-third  the  volume  of  the  chlorine  originally  in  the  tube. 
The  tube  may  be  previously  roughly  graduated  in  thirds  by 
rubber  rings,  allowance  being  made  for  the  space  occupied 
by  the  cork.  A  simpler  method  is  to  measure  the  distance 
from  the  base  of  the  cork  to  the  stop-cock  in  centimeters. 
The  residual  gas  will  measure  one-third  of  this  distance 
when  the  bulb  is  held  in  an  upright  position.  By  removing 
the  cork  the  gas  may  be  tested  and  shown  to  be  nitrogen  by 
extinguishing  a  splinter. 

A  glass  tube,  1  m.  long  and  15  to  20  mm.  in  diameter, 
sealed  at  one  end  and  fitted  with  a  one-holed  rubber  stopper 


AMMONIA  203 

through  which  the  stem  of  a  small  dropping-funnel  passes, 
may  be  used  in  case  the  eudiometer  is  not  at  hand.  The 
tube  is  filled  with  chlorine,  as  above,  inverted  with  the 
thumb  over  the  mouth  of  the  tube,  and  the  cork  on  the  stem 
of  the  dropping-funnel  quickly  thrust  into  the  open  end  of 
the  tube.  The  stem  of  the  droppinsj-funnel  should  have 
been  previously  filled  with  strongest  ammonium  hydroxide. 
The  funnel  is  then  filled  with  the  hydroxide,  and  a  few  cubic 
centimeters  allowed  to  fall  drop  by  drop  into  the  gas.  As 
each  drop  falls,  it  is  seen  to  emit  a  feeble  flash  of  light,  a 
phenomenon  not  observable  when  the  other  form  of  eudiom- 
eter is  used.  The  remaining  operations  are  identical  with 
those  described  above. 

2  NH3  +  3  CI2  =  6  HCl  4-  N2. 

NH3  -f  HCl  =  NH4CI. 

Eudiometer  (Fig.  11,  p.  26)  ;  CI  generator ;  glass  tube  sealed  at  one 
end,  1  m.  long,  15-20  mm.  diameter ;  dropping-funnel ;  rubber  stop- 
pers ;  strongest  NH4OH. 

36.  Decomposition  of  gaseous  ammonia  by  sodium  hypo- 
bromite  and  the  volumetric  relation  of  the  nitrogen  liber- 
ated.—  The  volumetric  relation  of  the  nitrogen  liberated 
from  a  given  volume  of  ammonia  by  the  action  of  sodium 
hypobromite  is  easily  shown  by  filling  the  eudiometer 
(Fig.  11,  p.  26)  with  dry  gaseous  ammonia  and  introducing 
a  strong  solution  of  sodium  hypobromite  through  the  stop- 
cock. The  eudiometer  must  be  perfectly  dry  and  is  filled 
with  ammonia,  either  by  conducting  the  gas  through  a  long 
glass  tube  thrust  up  into  the  eudiometer,  which  is  clamped 
in  a  vertical  position,  or  by  conducting  a  stream  of  the  dry 
gas  through  a  cork  inserted  in  the  funnel  bulb  at  the  top. 
In  the  latter  case  the  stop-cock  is  open  and  the  air  is  driven 
out  of  the  eudiometer  at  the  lower  opening.     Where  the 


204  CHEMICAL   LECTURE   EXPERIMENTS 

long  glass  tube  is  used  to  introduce  the  ammonia  it  must  be 
withdrawn  slowly  so  as  to  leave  the  eudiometer  completely- 
filled  with  the  gas.  A  perfectly  dry,  well-fitting  rubber  stop- 
per is  then  inserted  in  the  bottom  of  the  eudiometer  and 
a  strong  solution  of  sodium  hypobromite,  made  by  adding 
10  cc.  of  bromine  to  50  cc.  of  strong  sodium  hydroxide  solu- 
tion, poured  into  the  bulb.  The  stop-cock  is  carefully 
opened,  and  one  drop  of  the  hypobromite  solution  allowed 
to  enter  and  come  in  contact  with  the  gas.  Inasmuch  as 
there  will  probably  be  a  slight  pressure  inside  the  tube, 
caused  by  the  insertion  of  the  rubber  stopper,  a  bubble  or 
two  of  the  gas  may  escape.  As  soon  as  the  liquid  has 
entered  the  large  volume  of  gas,  rapid  absorption  takes 
place  and  the  hypobromite  solution  will  be  drawn  into  the 
tube.  Care  must  be  taken  to  allow  no  air  to  enter,  and 
accordingly  the  stop-cock  must  be  closed  before  all  the  liquid 
has  entered  the  eudiometer.  A  vigorous  evolution  of  nitro- 
gen will  take  place,  and  on  filling  the  bulb  with  water  and 
carefully  opening  the  stop-cock,  liquid  will  be  drawn  into 
the  tube  until  it  is  half  full.  The  residual  gas  may  be 
tested  by  inverting  the  eudiometer,  removing  the  stopper, 
and  inserting  a  burning  splinter.  From  two  volumes  of 
ammonia  one  volume  of  nitrogen  is  obtained. 

2  NHg  +  3  NaBrO  =  3  NaBr  +  3  HgO  +  Ng. 

Eudiometer  (Fig.  11,  p.  26);  rubber  stopper  ;  supply  of  dry  NH3  ; 
NaBrO  (10  cc.  Br,  60  cc.  NaOH  sol.). 

NITROGEN    CHLORIDE 

37.  Preparation.  —  When  chlorine  reacts  on  an  excess  of 
ammonia,  it  combines  with  the  hydrogen,  liberating  nitrogen 
(Ex.  35).  If,  however,  an  excess  of  chlorine  is  allowed 
to   act   on  ammonia  or  ammonium  chloride,  a  portion   of 


NITROGEN   IODIDE  205 

the  chlorine  unites  directly  with  the  nitrogen,  forming  a 
violently  explosive,  oily  liquid,  nitrogen  chloride.  The 
preparation  of  this  body  can  be  safely  carried  out  only 
on  a  very  small  scale. 

By  electrolyzing  a  solution  of  ammonium  chloride,  chlorine 
is  liberated  at  the  positive  pole,  and  in  the  nascent  condition 
reacts  with  the  excess  of  ammonium  chloride,  forming  small 
quantities  of  nitrogen  chloride.  The  electrolysis  must  be 
carried  out  in  an  open  vessel  (Fig.  36,  p.  74)  from  which 
the  graduated  tubes  have  been  removed.  The  electrodes, 
which  are  made  by  fusing  pieces  of  platinum  wire  into  bent 
glass  tubes  which  are  afterwards  filled  with  mercury,  are 
immersed  in  a  strong  solution  of  ammonium  chloride,  and 
the  current  from  4  or  5  cells  of  a  bichromate  battery  should 
be  passed  through  the  solution.  A  millimeter  layer  of  tur- 
pentine should  be  poured  on  the  surface  of  the  ammonium 
chloride  solution,  and  it  will  be  found  that  as  the  bubbles  of 
chlorine  ascend  they  will  carry  with  them  minute  quantities 
of  nitrogen  chloride,  which  on  coming  in  contact  with  the 
turpentine  will  explode.  As  the  explosion  may  at  times 
ignite  the  turpentine,  a  metal  plate  should  be  at  hand  with 
which  to  cover  the  dish  and  extinguish  the  flame.  Occa- 
sionally small  globules  of  nitrogen  chloride  will  settle  to 
the  bottom  of  the  dish ;  in  that  case  it  is  best  at  the  conclu- 
sion of  the  experiment  to  render  the  solution  strongly  alka- 
line with  ammonium  hydroxide  and  allow  it  to  stand  until 
the  nitrogen  chloride  has  of  itself  decomposed. 

Electrolytic  apparatus  (Fig.  36,  p.  74)  ;  battery. 

NITROGEN   IODIDE 

38.  Preparation.  —  (a)  When  iodine  is  allowed  to  act  on 
strong  ammonium  hydroxide,  a  portion  of  the  hydrogen  of 
the  ammonia  is  replaced  by  iodine,  forming  a  mixture  of 


206  CHEMICAL  LECTURE   EXPERIMENTS 

compounds  containing  nitrogen,  hydrogen,  and  iodine,  called 
nitrogen  iodide.  The  direct  precipitation  of  this  compound 
is  most  easily  effected  by  adding  to  a  concentrated  alcoholic 
solution  of  iodine  an  equal  volume  of  the  strongest  ammonia 
water.  The  nitrogen  iodide  is  immediately  precipitated  in 
the  form  of  a  black  powder. 

(b)  The  preparation  of  any  quantity  of  nitrogen  iodide 
is  best  secured  by  digesting  powdered  iodine  with  strongest 
ammonia  for  a  few  minutes.  A  few  crystals  of  iodine  are 
placed  in  a  mortar  and  pulverized.  Sufficient  strong  am- 
monia is  added  to  cover  the  iodine  completely,  and  the  mix- 
ture is  stirred  from  time  to  time.  After  a  few  minutes  the 
mixture  may  be  thrown  on  a  filter-paper,  washed  with  alco- 
hol, and  finally  with  water.  The  filter-paper  is  removed 
from  the  funnel  and  the  still  moist  precipitate  spread  on 
several  small  pieces  of  filter-paper  and  laid  on  a  porous  plate 
to  dry.  Without  the  application  of  artificial  heat  the 
material  will  require  about  one  hour  to  dry  sufficiently  to 
be  explosive. 

Porous  plates  ;  strongest  NH4OH  ;  powdered  I ;  alcohol. 

39.  Explosive  character  of  nitrogen  iodide.  —  The  great 
sensitiveness  of  this  compound  to  friction  or  heat  is  shown 
by  the  following  experiments. 

A  piece  of  filter-paper  on  which  a  small  quanity  of  nitro- 
gen iodide  has  been  dried  is  carefully  placed  on  a  table  and 
then  touched  with  a  feather.  Even  this  gentle  friction  is 
sufficient  to  cause  it  to  explode. 

A  piece  of  paper  containing  nitrogen  iodide  is  held  in 
crucible  tongs,  and  suddenly  depressed  over  a  Bunsen  flame. 
The  explosion  is  sufficent  to  blow  out  the  gas. 

A  moistened  filter-paper  on  which  nitrogen  iodide  has 
been  placed  is  stretched  tightly  over  the  mouth  of  a  7  cm. 
funnel.     After  drying,  the  nitrogen  iodide  may  be  exploded 


HYDROXYLAMINE  207 

with  a  feather.  The  explosion  will  blow  a  hole  through  the 
paper. 

A  dry  paper  containing  some  of  the  nitrogen  iodide  may 
be  exploded  on  a  moistened  filter-paper  stretched  over  the 
mouth  of  the  funnel  as  above. 

Nitrogen  iodide  may  be  exploded  by  a  sudden  puff  of  air. 
Air  is  blown  from  the  lungs  through  a  long  glass  tube  upon 
dry  nitrogen  iodide  on  a  piece  of  filter-paper.  The  nitrogen 
iodide  is  exploded.  Successive  papers  may  be  blown  on,  and 
though  the  papers  do  not  move,  the  iodide  will  be  exploded. 

A  peculiar  characteristic  of  the  explosion  produced  by 
the  nitrogen  iodide  is  its  inability  to  impart  its  explosion 
to  a  piece  of  dry  guncotton.  A  small  quantity  of  moist 
nitrogen  iodide  is  laid  on  a  small  piece  of  guncotton.  After 
the  iodide  has  become  thoroughly  dry,  it  may  be  exploded  by 
friction,  but  the  guncotton  will  be  unchanged.  The  com- 
bustible nature  of  the  guncotton  is  shown  by  applying  a 
flame. 

Nitrogen  iodide  on  filter-paper  ;  guncotton  ;  feather. 

HYDROXYLAMINE 

40.  Reduction  of  copper  sulphate  solution.  —  The  reducing 
action  of  hydroxylamine  on  an  alkaline  copper  solution  is 
shown  by  adding  sodium  hydroxide  in  excess  to  1  drop  of 
copper  sulphate  solution,  diluting  till  nearly  colorless,  and 
adding  a  few  drops  of  the  hydroxylamine  chloride  solution. 
On  heating  the  mixture,  a  yellow  precipitate  is  obtained. 
This  reaction  serves  as  a  very  delicate  test  for  hydroxyl- 
amine. 

Hydroxylamine  chloride  solution  ;  CUSO4  solution. 

41.  Alternate  reducing  and  oxidizing  action  on  iron  solu- 
tions. —  A  colorless  solution  of  ferrous  ammonium  sulphate 


208  CHEMICAL   LECTURE   EXPERIMENTS 

is  treated  with  sodium  hydroxide,  with  the  formation  of  the 
green  ferrous  hydroxide.  On  adding  a  few  drops  of  hy- 
droxy lamine  chloride  solution  to  the  ferrous  hydroxide  sus- 
pended in  the  alkaline  liquid,  the  precipitate  is  immediately 
turned  brown,  indicating  the  formation  of  ferric  hydroxide. 
Hydroxylamine  chloride,  when  acting  on. slightly  acid 
solutions  of  ferric  salts,  effects  their  reduction,  discharging 
the  color  of  the  solution.  A  portion  of  the  suspended  pre- 
cipitate from  the  above  experiment  is  treated  with  hydro- 
chloric acid  until  completely  dissolved,  any  great  excess  of 
acid  being  neutralized  with  sodium  hydroxide.  The  solution 
must,  however,  have  an  acid  reaction.  On  adding  hydroxyl- 
amine chloride  solution,  the  ferric  salt  is  reduced  and  the 
solution  becomes  colorless. 

Ferrous  ammonium  sulphate  solution  ;  hydroxylamine  chloride. 


NITROUS   OXIDE 

PREPARATION 

42.  By  heating  ammonium  nitrate.  —  Ammonium  nitrate 
on  heating  is  decomposed  quantitatively  into  nitrous  oxide 
and  water. 

Ten  grams  of  the  powdered  salt  are  heated  in  a  100  cc. 
Jena  glass  Erlenmeyer  flask  fitted  with  a  cork  and  a  wide 
delivery-tube.  The  salt  is  somewhat  hygroscopic,  and  hence 
it  is  advisable  to  dry  it  thoroughly  by  heating  in  an  air-bath 
to  120°.  A  considerable  quantity  of  the  salt  may  be  thus 
dried  and  preserved  in  well-stoppered  bottles.  On  heating, 
the  salt  first  melts  and  then  decomposes,  liberating  nitrous 
oxide.  As  the  liberation  of  the  gas  is  likely  to  be  somewhat 
violent,  a  wide  deli  very -tube  is  advisable.  In  heating,  care 
should  be  taken  to  heat  no  more  than  is  necessary  to  secure 
a  regular  flow  of  the  gas.     If  the  melted  salt  froths,  or  the 


NITROUS   OXIDE  209 

gas  evolution  is  too  great,  the  lamp  should  be  removed,  but 
replaced  before  water  can  rise  in  the  delivery -tube  and  fall 
into  the  hot  flask  and  break  it.  The  explosive  nature  of  the 
salt  requires  some  care  in  its  use,  though  if  the  previously 
dried  salt  is  used,  and  the  flame  is  turned  very  low,  the 
experiment  is  very  successful.  The  heating  should  be 
stopped  before  all  the  material  is  decomposed. 

Owing  to  the  solubility  of  nitrous  oxide  in  cold  water,  the 
water  in  the  pneumatic  trough  should  be  warmed  to  a  tem- 
perature of  between  30°  and  40°.  On  the  gradual  application 
of  heat,  the  gas  is  liberated,  and  may  be  collected  as  described. 
As  no  safety-tube  is  used  in  this  experiment,  it  is  advisable 
to  remove  the  delivery-tube  immediately  after  the  gas  has 
ceased  to  be  evolved. 

NH4NO3  =  2  H2O  +  N^O. 

100  cc.  Jena  glass  Erlenmeyer  flask  ;  wide  delivery-tube ;  pneumatic 
trough  ;  warm  water  ;  dried  NH4NO3. 


PROPERTIES 

43.  Combustion  of  a  splinter.  —  If  a  glowing  splinter  is 
thrust  into  a  cylinder  of  nitrous  oxide,  it  is  immediately 
rekindled  and  burns  with  a  degree  of  intensity  similar  to 
that  of  its  combustion  in  pure  oxygen. 

Occasionally,  in  preparing  the  nitrous  oxide,  considerable 
quantities  of  free  nitrogen  are  formed  which  diminish  to  a 
marked  degree  the  activity  of  this  gas  in  supporting  com- 
bustion. The  presence  of  nitrogen  first  effects  the  rekindling 
of  a  glowing  splinter.  If  the  gas  relights  the  splinter,  it  is 
an  indication  of  its  purity.  A  burning  splinter  will,  how- 
ever, always  burn  with  increased  brilliancy  in  the  gas,  even 
if  somewhat  contaminated  with  nitrogen. 

Cylinder  of  N2O  ;  splinter. 

p 


210  CHEMICAL   LECTURE   EXPERIMENTS 

44.  Combustion  of  hydrogen.  —  Hydrogen  is  allowed  to 
burn  from  the  recurved  jet  (Fig.  41,  p.  85)  and  is  then 
lowered  into  a  cylinder  of  nitrous  oxide.  The  flame  under- 
goes a  marked  change  in  color,  becoming  covered  with  a  blue 
envelope.  The  presence  of  nitrous  acid  after  the  combustion 
is  shown  by  thrusting  a  piece  of  iodo-starch  paper  into  the 
cylinder,  where  it  is  instantly  turned  blue. 

Recurved  jet  (Fig.  41,  p.  85)  ;  cylinder  of  N2O  ;  H  supply  ;  KI- 
starch  paper. 

45.  Explosion  of  hydrogen  and  nitrons  oxide.  —  A  thick- 
walled  cylinder  is  half  filled  over  warm  water  with  nitrous 
oxide,  the  remaining  volume  being  filled  with  hydrogen. 
The  cylinder  is  covered  with  a  glass  plate  and  a  towel 
wrapped  around  it.  On  the  application  of  a  lighted  taper 
an  explosion  occurs. 

N2O  H-  H2  =  H2O  -t-  N2. 

Cylinder  ;  pneumatic  trough  filled  with  warm  water ;  H  generator ; 
N2O  supply. 

46.  Combustion  of  sulphur.  —  Sulphur,  burning  feebly  in 
a  deflagrating-spoon,  when  lowered  into  a  cylinder  of  nitrous 
oxide,  is  extinguished.  If,  however,  it  is  strongly  heated 
and  brought  almost  to  a  boil  before  being  introduced,  it  will 
burn  brilliantly,  forming  sulphur  dioxide. 

8+2^20  =  802  +  2^2. 
Jar  of  N2O  ;  sulphur  in  deflagrating-spoon. 

47.  Combustion  of  phosphorus.  —  A  small  piece  of  phos- 
phorus is  placed  in  the  deflagrating-spoon,  and  after  being 
ignited  is  quickly  thrust  into  a  jar  of  nitrous  oxide.  The 
combustion,  similar  to  that  in  pure  oxygen,  continues  with 
great  brilliancy. 

Jar  of  N2O  ;  P. 


NITRIC    OXIDE  211 

48.  Combustion  of  iron.  —  A  cylinder  or  tall  beaker,  hav- 
ing a  piece  of  asbestos  paper  or  wire  gauze  in  the  bottom,  is 
filled  with  nitrous  oxide.  A  bundle  of  iron  wires,  tipped 
with  a  bit  of  molten  sulphur,  is  ignited  and  lowered  into 
the  jar.  The  combustion  proceeds  with  great  brilliancy, 
the  particles  of  molten  iron  oxide  falling  to  the  bottom  and 
striking  on  the  asbestos.  It  is  advisable  to  have  a  centi- 
meter layer  of  water  on  the  bottom  of  the  cylinder. 

Cylinder  with  ashestos  in  bottom,  filled  with  N2O ;  bundle  of  iron 
wires  tipped  with  sulphur. 

NITRIC    OXIDE 

PREPARATION 

49.  From  nitric  acid  and  copper.  —  The  action  of  copper 
on  dilute  nitric  acid  results  in  the  formation  of  nitric  oxide. 

To  prepare  this  gas,  copper  clippings  are  placed  in  a 
500  cc.  Erlenmeyer  flask  fitted  with  a  thistle-tube  and  a 
delivery  tube,  the  thistle-tube  extending  to  the  bottom  of 
the  flask.  The  copper  is  covered  with  water,  and  concen- 
trated nitric  acid  added  through  the  thistle-tube.  The  gas 
is  evolved  without  the  aid  of  heat  and  may  be  collected 
at  the  pneumatic  trough.  If  the  gas  evolution  is  too  violent, 
water  is  added  through  the  thistle-tube  to  dilute  the  acid. 
If,  on  the  other  hand,  the  flow  of  gas  is  slow,  concentrated 
nitric  acid  is  added.  After  the  reaction  has  been  running 
for  a  few  minutes  the  gaseous  contents  of  the  flask  become 
colorless,  while  any  of  the  gas  escaping  into  the  air  has  a 
deep  reddish  brown  color.  The  cylinders  of  gas  collected 
at  the  pneumatic  trough  are  also  colorless. 

Provision  must  be  made  for  conducting  the  excess  of  gas 
into  a  hood,  as  the  fumes  are  very  irritating. 

3  Cu  -1-  8  HNO3  =  3  Cu(N0^)2  -f  4  H2O  -t-  2  NO. 

500  cc.  Erlenmeyer  flask ;  Cu  clippings  ;  thistle-tube  and  glass  elbow. 


212  CHEMICAL  LECTUBB  EXPERIMENTS 

50.  By  the  action  of  sulphuric  acid  on  copper  and  potas- 
sium nitrate  solution.  —  Instead  of  adding  nitric  acid  directly 
to  copper,  the  acid  may  be  formed  by  adding  sulphuric  acid 
to  a  strong  solution  of  a  nitrate  covering  a  quantity  of 
copper  clippings. 

Copper  clippings  in  the  bottom  of  an  Erlenmeyer  flask 
are  covered  with  a  saturated  solution  of  potassium  nitrate. 
Concentrated  sulphuric  acid  is  allowed  to  drop  from  a  drop- 
ping-funnel  upon  the  liquid.  A  steady  evolution  of  nitric 
oxide  is  obtained,  the  rate  of  which  is  determined  by  the 
dropping  of  the  sulphuric  acid. 

2  KNO3  +  H2SO4  =  K2SO4  +  2  HNO3. 

3  Cu  +  8  HNO3  =  3  Cu(N03)2  4-  4  H2O  4-  2  NO. 

Apparatus  (Fig.  3,  p.  11)  ;  Erlenmeyer  flask  ;  dropping-funnel ; 
saturated  solution  of  KNO3  ;  Cu  clippings. 

51.  From  sodium  nitrite  and  acidulated  ferrous  chloride. — 

When  a  strong  solution  of  sodium  nitrite  is  allowed  to  drop 
into  a  solution  of  ferrous  chloride  to  which  hydrochloric 
acid  has  been  added,  a  regular  evolution  of  nitric  oxide  is 
obtained. 

A  handful  of  iron  nails  is  placed  in  a  500  cc.  Erlenmeyer 
flask  and  covered  with  200  cc.  of  concentrated  hydrochloric 
acid,  and  the  flask  is  allowed  to  stand  over  night.  Suffi- 
cient ferrous  chloride  will  have  been  formed  during  this 
time  to  give  a  strong  evolution  of  nitric  oxide  with  sodium 
nitrite.  A  two-holed  rubber  stopper  fitted  with  a  drop- 
ping-funnel containing  a  saturated  solution  of  sodium 
nitrite  and  a  delivery-tube  is  inserted  in  the  neck  of 
the  flask. 

500  cc.  Erlenmeyer  flask  ;  dropping-funnel ;  cork  and  delivery-tube  ; 
iron  nails  ;  saturated  solution  of  NaN02. 


NITRIC    OXIDE  213 


PROPERTIES 

52.  Neutrality  of  pure  nitric  oxide  to  litmus.  —  A  stream 
of  nitric  oxide  is  conducted  through  a  clean  delivery-tube 
under  a  cylinder  inverted  over  a  crystallizing  dish  of  water. 
The  water  should  be  neutral  and  the  cylinder  should  not  be 
completely  filled,  the  supply  of  nitric  oxide  being  cut  off  that 
it  may  not  come  in  contact  with  the  air,  thereby  turning  the 
liquid  slightly  acid.  A  piece  of  blue  litmus  paper  fastened 
to  the  end  of  a  copper  wire  is  then  pushed  up  into  the  inte- 
rior of  the  flask,  care  being  taken  that  no  air  is  admitted. 
No  change  will  be  observed  in  the  blue  litmus  until  a  small 
quantity  of  air  is  admitted.  The  nitrogen  peroxide  formed 
will  then  turn  the  litmus  red. 

NO  generator  ;  cylinder  and  crystallizing  dish  ;  pure  neutral  water ; 
blue  litmus  paper ;  copper  wire. 

53.  Solubility  in  ferrous  sulphate  solution.  —  Nitric  oxide 
is  collected  in  the  eudiometer  (Fig.  11,  p.  26),  and  ferrous 
sulphate  solution  allowed  to  flow  slowly  through  the  gas  by 
opening  the  stop-cock.  The  nitric  oxide  is  rapidly  absorbed, 
the  solution  becoming  a  dark  brown. 

To  prepare  a  considerable  quantity  of  a  solution  of  nitric 
oxide  in  ferrous  sulphate,  the  gas  is  conducted  into  a  gas 
washing-bottle  containing  a  solution  of  ferrous  sulphate  or 
ferrous  ammonium  sulphate  (Mohr's  salt).  In  case  the  lat- 
ter is  used,  the  color  change  is  more  noticeable ;  for  the  salt 
solution  before  the  introduction  of  the  gas  is  colorless,  while 
as  the  gas  is  absorbed,  the  color  passes  rapidly  to  a  very 
dark  brown. 

On  heating  the  liquid,  nitric  oxide  is  again  liberated. 

Eudiometer  (Fig.  11,  p.  26);  gas  washing-bottle;  NO  generator; 
FeS04  solution  ;  (NH4)2Fe  (804)2  solution. 


214  CHEMICAL  LECTURE  EXPERIMENTS 

54.  Absorption  by  nitric  acid.  —  (a)  Nitric  oxide  is  absorbed 
by  nitric  acid,  with  the  formation  of  nitrous  acid  and  nitro- 
gen peroxide.  The  variation  in  the  nature  of  the  products 
formed  corresponds  to  the  variations  in  strength  of  the 
nitric  acid  used. 

Three  gas  washing-bottles  are  connected  in  series  and 
nitric  oxide  allowed  to  pass  through  them.  The  first  bottle 
contains  nitric  acid  of  a  specific  gravity  of  1.25;  the  second, 
nitric  acid  of  the  specific  gravity  of  1.35 ;  and  the  last,  acid 
of  the  specific  gravity  of  1.5.  The  gas  issuing  from  the 
last  bottle  is  then  conducted  into  a  flue.  On  allowing  the 
nitric  oxide  to  pass  through  this  system  for  some  time,  a 
series  of  color  changes  is  observed  in  the  different  bottles. 
The  first  bottle  contains  nitrous  anhydride  and  nitrous  acid, 
and  will  acquire  a  blue  color,  especially  if  cooled  in  a  beaker 
of  ice-water.  The  second  will  possess  a  green  color  and  the 
last  the  deep  brown  color  of  fuming  nitric  acid. 

Three  gas  washing-bottles  ;  NO  generator  ;  HNOs  of  1.25, 1.35,  and 
1.5  specific  gravities  ;  ice. 

(6)  Nitric  oxide  is  collected  in  the  eudiometer  (Fig.  11, 
p.  26)  over  water  and  concentrated  (not  fuming)  nitric  acid 
is  allowed  to  flow  down  into  the  gas  through  the  stop-cock. 
The  absorption  is  quite  rapid,  as  is  indicated  by  the  rise  of 
the  liquid  in  the  tube. 

Eudiometer  (Fig.  11,  p.  26)  ;  NO  generator;  con.  HNO3. 

55.  Absorption  by  acidulated  potassium  permanganate 
solution.  —  Nitric  oxide  is  oxidized  to  nitric  acid  by  potas- 
sium permanganate  in  the  presence  of  sulphuric  acid.  The 
absorption  of  the  gas  and  the  decolorization  of  the  per- 
manganate solution  may  be  shown  by  collecting  a  quantity 
of  the  nitric  oxide  in  the  eudiometer  (Fig.  11,  p.  26)  and 
allowing  a  solution  of   potassium   permanganate,  strongly 


NITRIC   OXIDE  215 

acidulated  with  sulphuric  acid,  to  flow  slowly  down  through, 
the  gas. 

6  KMn04  +  9  HgSO^  +  10  NO  =  10  HNO3  +  3  K2SO4 

+  6MnS04-f-4H20. 

Eudiometer  (Fig.  11,  p.  26)  ;  NO  supply  ;  KMnO*  +  H2SO4. 

56.  Nitric  oxide  and  air.  — A  tall  glass  cylinder  filled  with 
nitric  oxide  and  covered  with  a  glass  plate  is  placed  mouth 
upwards  on  the  table.  A  cylinder  filled  with  air  is  placed 
mouth  downward  on  top  of  the  glass  plate  covering  the 
cylinder  of  nitric  oxide.  On  slipping  out  the  glass  plate 
between  the  two  cylinders  red  fumes  appear  where  the  air 
and  nitric  oxide  come  in  contact.  As  the  nitrogen  peroxide 
formed  is  much  heavier  than  either  air  or  nitric  oxide,  the 
experiment  is  especially  interesting  in  showing  the  diffusi- 
bility  of  the  gases. 

Cylinder  of  NO  ;  empty  cylinder. 

57.  Union  with  pure  oxygen.  —  Nitric  oxide  unites  with 
pure  oxygen  quantitatively,  forming  nitrogen  peroxide.  In 
this  union  a  contraction  takes  place,  as  two  volumes  of  nitric 
oxide  combine  with  one  volume  of  oxygen  to  form  two 
volumes  of  nitrogen  peroxide. 

A  liter  bottle  is  fitted  with  a  two-holed  rubber  stopper 
carrying  a  straight  glass  tube  extending  to  within  7  cm.  of 
the  bottom  of  the  bottle  and  drawn  out  to  a  jet  2  mm.  in 
diameter.  A  glass  elbow  is  thrust  through  the  second  hole 
of  the  rubber  stopper.  Kubber  tubes  and  pinch-cocks  are 
slipped  on  the  ends  of  both  glass  tubes,  and  the  rubber  stop- 
per and  fittings  thrust  under  water  into  the  mouth  of  the 
bottle,  which  has  previously  been  three-fourths  filled  with 
nitric  oxide  at  the  pneumatic  trough  (Fig.  90).  Both 
pinch-cocks  being  closed,  the  apparatus  is  supported  mouth 


216 


CHEMICAL  LECTURE  EXPERIMENTS 


K'ni 


downwards,  and  a  glass  tube  dipping  into  a  beaker  of  blue 
litmus  solution  is  connected  with  the  rubber  tube  connected 
with  the  jet  in  the  bottle.  Oxygen  under  pressure,  prefer- 
ably from  a  cylinder  of  the  compressed  gas,  is  forced  through 
the  glass  elbow  after  opening  the  pinch- 
cock  until  a  few  bubbles  have  entered 
the  bottle.  As  each  bubble  of  the  oxy- 
gen comes  in  contact  with  the  nitric 
oxide,  red  fumes  of  nitrogen  peroxide 
will  appear.  These  are  soon  dissolved 
by  the  water  remaining  in  the  bottle, 
-^c^         ^tta  ^^^  tl^^  g^s  again  becomes  clear.     The 

process  is  repeated  a  number  of  times, 
and  finally  the  pinch-cock  connecting 
the  glass  jet  with  the  blue  litmus  solu- 
FiG.  90  *^^^   ^^   opened.      On   account   of   the 

vacuum  inside  the  flask  caused  by  the 
solubility  of  nitrogen  peroxide  in  water,  the  blue  litmus 
solution  will  rise  rapidly  through  the  jet  and  enter  the 
flask  in  the  form  of  a  fountain.  There  in  the  presence  of 
acid  fumes  the  color  will  be  turned  from  blue  to  red. 

Apparatus  (Fig.  90)  ;  liter  bottle  ;  rubber  stopper  (2-holed)  ;  pinch- 
cocks  and  tubes  ;  0  supply  ;  blue  litmus  solution. 


58.  Combustion  in  nitric  oxide.  —  A  glowing  or  burning 
splinter  when  thrust  into  nitric  oxide  is  extinguished. 

A  burning  candle  on  being  lowered  into  nitric  oxide  is 
extinguished. 

Burning  sulphur  on  a  deflagrating-spoon  is  extinguished 
when  lowered  into  the  gas. 

Phosphorus  when  feebly  burning  on  a  deflagrating-spoon 
is  likewise  extinguished  when  lowered  into  nitric  oxide. 

If,  however,  a  piece  of  phosphorus  is  placed  on  a  defla- 
grating-spoon and  allowed  to  burn  vigorously  in  the  air  and 


NITRIC    OXIDE  217 

is  then  lowered  into  the  nitric  oxide,  the  heat  generated  by- 
its  combustion  is  sufficient  to  dissociate  the  gas,  and  con- 
sequently the  combustion  proceeds  even  more  vigorously 
than  in  air. 

Jars  of  NO  ;  deflagrating-spoons  ;  candle  ;  P  ;  S. 

59.  Combustion  of  charcoal. —  A  piece  of  charcoal  fastened 
to  a  stout  iron  wire  is  heated  to  glowing  in  a  Bunsen  flame. 
On  thrusting  it  into  a  cylinder  of  nitric  oxide  the  flame  is 
extinguished. 

If,  however,  the  charcoal  is  placed  in  a  bulb-tube  and 
strongly  heated  with  a  Bunsen  flame,  it  will  glow  in  a  cur- 
rent of  nitric  oxide.  Provision  should  be  made  for  con- 
ducting the  escaping  gas  into  a  flue. 

NO  generator  ;  jar  of  NO  ;  bulb-tube  ;  charcoal. 

60.  Combustion  of  carbon  disulphide.  —  When  the  vapor 
of  carbon  disulphide  is  mixed  with  nitric  oxide  and  the 
mixture  ignited,  a  characteristic  blue  flame  is  produced 
which  has  great  actinic  power,  and  has  consequently  been 
used  as  artificial  illumination  for  taking  photographs. 

Three  or  four  cubic  centimeters  of  carbon  disulphide  are 
rapidly  poured  from  a  test-tube  into  a  250  cc.  cylinder  of 
nitric  oxide  covered  with  a  plate.  The  glass  plate  is 
slipped  to  one  side  to  permit  the  introduction  of  the 
carbon  disulphide,  and  then  the  cylinder  is  immediately 
closed.  The  cylinder  is  then  thoroughly  shaken  to  mix 
the  vapors,  the  glass  plate  removed,  and  the  mixture 
ignited. 

A  blue  flame  results,  the  sulphur  being  deposited  on  the 
sides  of  the  vessel.  The  cylinder  should  be  immediately 
washed,  as  otherwise  the  sulphur  will  be  hard  to  remove. 

Jar  of  NO  ;  CSg. 


218  CHEMICAL   LECTURE   EXPERIMENTS 

NITROUS  ANHYDRIDE  AND  NITROUS  ACID 

61.  Preparation  of  nitrous  anhydride  from  arsenic  trioxide 
and  nitric  acid.  —  When  arsenic  trioxide  is  oxidized  by  nitric 
acid  of  a  specific  gravity  of  from  1.3  to  1.35,  gaseous  nitrous 
anhydride  is  liberated. 

Twenty-five  grams  of  arsenic  trioxide  are  placed  in  a 
250  CO.  flask  fitted  with  a  thistle-tube  and  an  elbow.  The 
arsenic  is  covered  with  nitric  acid  of  the  above-mentioned 
specific  gravity  and  the  mixture  gently  warmed.  The  gas 
is  heavy,  and  may  be  collected  by  displacement  in  a  large 
flask.  When  collected  in  this  manner,  the  deep  reddish 
brown  color  is  very  noticeable. 

2  AsA  -f  4  HNO3  -f  4  H2O  =  4  H3ASO4  +  2  NA- 

250  cc.  flask  ;  thistle-tube  and  elbow  ;  large  flask ;  HNO3  specific 
gravity  1.3-1.35 ;  AS2O3. 

62.  Liquefaction  of  nitrous  anhydride.  —  The  gaseous 
nitrous  anhydride  obtained  from  the  preceding  experiment 
is  passed  successively  through  a  gas  washing-bottle  im- 
mersed in  a  beaker  of  cold  water  to  condense  the  steam 
formed  by  the  reaction,  and  then  through  a  U-tube  packed 
in  a  freezing-mixture  of  ice  and  salt.  The  water  in  the  first 
beaker  must  not  be  below  8°  C.  On  removing  the  U-tube 
from  the  freezing-mixture  a  blue  liquid  will  be  found ;  but  as 
some  nitrogen  peroxide  often  condenses  with  it,  the  color  is 
not  always  clear.  On  the  addition  of  a  small  quantity  of  ice- 
water,  the  color  immediately  appears  perfectly  blue.  The 
liquid  boils  readily  on  the  application  of  a  very  gentle  heat. 

N2O3  supply  ;  gas  washing-bottle  ;  U-tube ;  freezing-mixture  of  ice 
and  salt. 

63.  Phenylenediamine  reaction  for  nitrous  acid.  —  Phe- 
nylenediamine  solution,  when  added  to  a  solution  of  sodium 
nitrite,  to  which  a  few  drops  of  sulphuric  acid  have  been 
added,  gives  an  intense  orange-yellow  color. 


NITROGEN   PEROXIDE 


219 


The  delicacy  of  this  reaction  is  so  great  as  to  make  its  use 
of  great  importance  in  determining  minute  quantities  of 
nitrites  in  potable  waters.  A  few  drops  of  acidulated 
sodium  nitrite  solution  are  added  to  2  1.  of  water  in  a  large 
beaker.  On  the  addition  of  a  few  drops  of  phenylenediamine 
solution,  a  distinct  yellow  coloration  will  appear  even  at  this 
great  dilution. 

NaN02 ;  phenylenediamine  solution. 


NITROGEN    PEROXIDE 

PREPARATION 

64.  By  ignition  of  lead  nitrate.  —  Lead  nitrate  on  ignition 
is  decomposed  into  lead  monoxide,  nitrogen  peroxide,  and 
oxygen.  Nitrogen  peroxide,  being  easily  condensed,  is  re- 
tained in  a  U-tube  packed  in  salt  and  ice,  while  the  oxygen 
is  collected  at  the  pneumatic  trough. 

Fifty  grams  of  previously  dried  lead  nitrate  are  placed  in 
a  200  cc.  Jena  glass  distilling  flask,  connected  to  one  limb 
of  a  U-tube  packed  in  ice  and 
salt;  the  other  limb  is  fitted 
with  a  cork  and  a  delivery-tube 
leading  to  the  pneumatic  trough 
(Fig.  91).  The  neck  of  the  dis- 
tilling flask  is  securely  corked, 
and  the  lead  nitrate  carefully 
heated  with  a  Bunsen  burner. 
After  all  the  air  has  been  driven 
out  of  the  apparatus,  the  oxy- 
gen may  be  collected  and  tested 
at  the  pneumatic  trough.  On 
disconnecting  the  apparatus,  the  impure  nitrogen  peroxide 
will  be  found  as  a  red  liquid  condensed  in  the  U-tube.     The 


1 

&-i 

y 

y 

1  s 

^m 

Fig.  91 


220  CHEMICAL   LECTURE   EXPERIMENTS 

lead  nitrate  used  for  this  experiment  should  be  dried  by 
heating  in  a  porcelain  evaporating-dish  till  red  fumes  just 
appear. 

200  cc.  Jena  glass  distilling-flask  ;  U-tube  in  freezing-mixture  ;  dried 
pulverized  Pb(N03)2. 

65.   By  the  action  of  tin  on  concentrated  nitric  acid.  —  Tin 

and  nitric  acid  react  vigorously,  nitrogen  peroxide  being 
evolved. 

The  bottom  of  a  300  cc.  Erlenmeyer  flask  is  covered  with 
granulated  tin,  and  strong  nitric  acid  is  introduced  through 
a  thistle-tube  reaching  to  the  bottom  of  the  flask.  A  glass 
elbow  thrust  through  the  cork  in  the  neck  of  the  flask  is 
connected  to  a  gas  washing-bottle,  which  is  in  turn  con- 
nected with  a  U-tube  immersed  in  a  freezing-mixture  of 
salt  and  ice.  As  soon  as  the  acid  is  added,  the  reaction  be- 
gins and  great  heat  is  developed.  Most  of  the  steam  formed 
is  condensed  in  the  gas  washing-bottle.  The  nitrogen  per- 
oxide is  condensed  in  the  U-tube.  By  disconnecting  the 
U-tube  and  connecting  a  glass  tube  to  the  gas  washing-bottle, 
the  gas  may  be  collected  by  displacement. 

5  Sn  +  20  HNO3  =  SnA  (OH)io  -f  5  HgO  +  20  NO^.     [?] 

300  cc.  Erlenmeyer  flask ;  thistle-tube  and  glass  elbow ;  2-holed 
cork ;  gas  washing-bottle  ;  U-tube  ;  freezing-mixture  ;  Sn. 


PROPERTIES 

66.   Vaporization  of  liquid  nitrogen  peroxide.  —  A  few 

drops  of  liquid  nitrogen  peroxide  are  placed  in  a  flask,  the 
bottom  of  which  is  warmed  with  the  hand.  The  liquid 
immediately  evaporates,  filling  the  flask  with  deep  brownish 
red  fumes. 

250  cc.  flask ;  liquid  NO2. 


NITROGEN    PEROXIDE  221 

67.  Dilution  of  fuming  nitric  acid.  —  On  diluting  fuming 
nitric  acid  with  water  the  excess  of  nitrogen  peroxide  in  the 
nitric  acid  undergoes  decomposition  in  the  presence  of  water, 
forming  nitrous  anhydride,  the  various  steps  in  the  dilution 
being  characterized  by  color  changes  in' the  solution. 

Twenty  cubic  centimeters  of  fuming  nitric  acid  in  a  beaker 
are  gradually  diluted  with  water„  The  reddish  brown  acid 
becomes  light  yellow  and  then  green.  If  the  green  solution 
is  cooled  with  ice,  a  blue  color  will  be  obtained. 

The  reverse  of  this  operation  may  be  carried  out  by  grad- 
ually adding  to  some  crushed  ice  in  a  beaker  fuming  nitric 
acid.  In  this  case  the  solution  becomes  first  blue,  then 
green,  light  yellow,  and  finally  dark  brown. 

Fuming  HNO3 ;  ice. 

68.  Combustion  of  charcoal.  —  Glowing  charcoal  when  in 
contact  with  liquid  nitrogen  peroxide  burns  brilliantly  in  the 
oxygen  liberated  from  this  compound. 

Two  cubic  centimeters  of  liquid  nitrogen  peroxide  are 
placed  in  a  test-tube  clamped  in  a  vertical  position.  A 
piece  of  charcoal  fastened  to  one  end  of  an  iron  wire  and 
brought  to  a  glow  in  a  Bun  sen  flame  is  carefully  lowered  till 
it  just  touches  the  surface  of  the  liquid.  It  continues  to 
burn  with  increased  brilliancy. 

Liquid  NO2  ;  piece  of  charcoal. 

69.  Combustion  of  potassium  in  gaseous  nitrogen  peroxide. 

—  Potassium  combines  with  the  oxygen  of  nitrogen  perox- 
ide, burning  with  considerable  brilliancy. 

A  3  mm.  piece  of  potassium  is  placed  in  a  deflagrating- 
spoon,  slightly  warmed,  and  lowered  into  a  cylinder  of 
nitrogen  peroxide  having  a  layer  of  sand  at  the  bottom. 
The  potassium  takes  tire  and  burns  brilliantly. 

Jar  of  NO2  ;  deflagrating- spoon  ;  K. 


222 


CHEMICAL  LECTURE  EXPERIMENTS 


mr- 


70.  Absorption  of  nitrogen  peroxide  by  sulphuric  acid. 
(Formation  of  chamber  crystals.) —  The  formation  of  nitrogen 
peroxide  and  the  subsequent  absorption  of  this  compound  by 
sulphuric  acid  is  shown  by  conducting 
nitric  oxide  from  a  suitable  generator  into 
a  large  flask,  the  sides  of  which  have 
been  moistened  with  concentrated  sul- 
phuric acid.  A  two-holed  rubber  stopper 
in  the  neck  of  the  flask  contains  a  glass 
tube  extending  halfway  to  the  bottom 
of  the  flask  and  a  short  glass  elbow  which 
is  connected  with  the  draft  or  flue. 

Nitric  oxide  is  conducted  through  the 
long  glass  tube  into  the  flask,  where  it 
combines  with  the  oxygen  of  the  air,  form- 
ing the  deep  red  fumes  of  nitrogen  per- 
oxide, which  are  immediately  absorbed  by 
the  sulphuric  acid.      The  whole  interior  of  the  flask  be- 
comes covered  with  a  crystalline  deposit  of  chamber  crystals 
(Fig.  92). 

Large  flask  (2-6  1.);  NO  generator. 


NITRIC  ACID 


PREPARATION 

71.  From  potassium  nitrate  and  sulphuric  acid.  —  The  gen- 
eral principle  of  using  a  strong  acid  to  drive  a  weaker  out  of 
combination  is  made  use  of  in  the  preparation  of  nitric  acid. 
Thirty  grams  of  powdered  potassium  nitrate  are  placed  in  a 
500  cc.  glass-stoppered  retort  and  18  cc.  of  concentrated  sul- 
phuric acid  are  carefully  poured  through  a  funnel  upon  the 
mixture,  care  being  taken  to  prevent  any  acid  from  getting 
into  the  neck  of  the  retort.     The  retort  is  then  gently  agi- 


NITRIC    ACID 


223 


tated  to  insure  a  thorough  mixture  of  the  ingredients.  It  is 
then  clamped  so  that  it  may  be  heated  on  a  wire  gauze,  its 
neck  being  thrust  deep  into 
a  500  cc.  flask  partially  im- 
mersed in  water  in  a  large 
crystallizing-dish  (Fig.  93). 
On  applying  a  very  gentle 
heat,  nearly  colorless  nitric 
acid  distils  over  and  con- 
denses in  the  flask. 


KNOg  -f  H2SO4 

=  KHSO4  +  HNO3. 


Fig.  93 


500  cc.  glass-stoppered  retort ;  500  cc.  flask ;  crystallizing-dish  ; 
KNOa. 

PROPERTIES 

72.  Intense  acid  reaction.  — Nitric  acid  possesses  a  strong 
acid  reaction  which  is  readily  shown  by  dipping  a  glass  rod 
into  fuming  nitric  acid  and  then  into  a  beaker  containing 
a  liter  of  water.  Even  at  this  great  dilution  the  acidified 
water  will  instantly  redden  a  strip  of  blue  litmus  paper. 

73.  Action  on  organic  matter.  —  Nitric  acid  attacks  organic 
matter,  especially  that  of  an  animal  nature,  staining  it  yel- 
low. The  simplest  example  of  this  property  of  nitric  acid 
is  the  familiar  fact  that  the  acid  stains  the  fingers  yellow. 
A  large  white  feather  has  approximately  the  same  composi- 
tion as  the  human  skin,  and  when  dipped  into  fuming  nitric 
acid  in  a  beaker  is  stained  a  brilliant  yellow,  while  a  con- 
siderable portion  of  the  feather  is  actually  destroyed.  On 
washing  off  the  excess  of  acid  and  dipping  the  feather  into 
dilute  ammonium  hydroxide,  the  color  is  somewhat  intensi- 
fied and  becomes  fixed. 

Acid  spots  on  clothing,  if  caused  by  sulphuric  or  hydro- 


224  CHEMICAL   LECTURE   EXPERrMENTS 

chloric  acid,  are  easily  effaced  by  moistening  with  ammo- 
nium hydroxide.  Spots  resulting  from  the  action  of 
nitric  acid,  however,  cannot  be  removed. 

Large  white  feather  ;  fumhig  HNO3. 

74.  Action  on  turpentine.  —  Strongest  nitric  acid  oxidizes 
turpentine,  even  in  the  cold,  with  such  rapidity  as  to  ignite 
the  hydrocarbon. 

A  small  evaporating  dish  is  placed  on  a  layer  of  sand  in 
the  bottom  of  a  1  or  2  1.  beaker  and  one-third  filled  with 
a  mixture  of  equal  volumes  of  fuming  nitric  acid  and  con- 
centrated sulphuric  acid.  This  mixture  is  easily  secured  by 
slowly  pouring  5  cc.  of  concentrated  sulphuric  acid  into  an 
equal  volume  of  fuming  nitric  acid  held  in  a  test-tube,  keep- 
ing the  test-tube  cool  if  necessary  under  the  water  tap, 
though  care  should  be  taken  not  to  get  any  water  in  the 
mixture  of  acids.  A  few  drops  of  turpentine  are  drawn  up 
into  a  long  (1  m.)  glass  tube  with  an  elbow  at  one  end, 
the  short  arm  (15  cm.)  of  which  is  drawn  out  to  a  point 
(Fig.  50,  p.  102).  By  raising  the  thumb  from  the  open  end 
of  the  tube  the  turpentine  is  allowed  to  drop  on  the  acid 
mixture  in  the  evaporating-dish.  As  each  drop  comes  in 
contact  with  the  acid,  it  bursts  into  flame.  Care  should 
be  taken  to  prevent  any  drops  of  acid  from  flying  out  of  the 
beaker,  and  provision  should  be  made  for  carrying  off  the 
vapors  rising  from  the  combustion. 

2  1.  beaker  ;  small  evaporating-dish  ;  long  bent  glass  tube  ;  fuming 
HNO3  ;  cone.  H2SO4  ;  turpentine. 

75.  Action  on  sawdust.  —  Sawdust  is  heated  in  a  small 
evaporating-dish  till  it  is  just  about  to  char,  and  3  cc.  of 
fuming  nitric  acid  are  poured  upon  the  mass.  The  carbo- 
naceous material  is  immediately  oxidized  and  the  mixture 
undergoes  a  vigorous  combustion. 


NITRIC    ACID  225 

76.  Action  on  sugar.  —  Nitric  acid  does  not  act  upon 
sugar  in  the  cold,  as  may  be  seen  by  pouring  5  cc.  of  the 
acid  over  2  g  of  sugar  in  the  bottom  of  a  test-tube.  On 
warming  the  mixture,  however,  a  violent  reaction  takes 
place,  the  sugar  being  oxidized 

77.  Action  on  wood,  carbon  disulphide,  and  illuminating 
gas.  —  The  vigorous  oxidizing  action  of  nitric  acid  is  best 
shown  when  the  acid  is  freshly  prepared  by  heating  a  mix- 
ture of  potassium  nitrate  and  sulphuric  acid.  Such  a  mixture 
is  heated  in  a  small  wide-mouthed  flask  and  a  glowing 
sj)linter  thrust  into  the  liquid.  The  wood  is  instantly 
ignited  and  burns  brightly. 

If  a  few  drops  of  carbon  disulphide  are  poured  from  a 
test-tube  into  the  flask  and  a  flame  held  instantly  at  the 
mouth,  combustion  ensues  in  a  most  brilliant  manner,  the 
carbon  disulphide  burning  with  a  deep  blue  flame. 

A  slow  stream  of  illuminating  gas  passing  through  a  long 
bent  glass  tube  is  ignited  and  thrust  into  the  neck  of  the 
flask.     Combustion  proceeds  vigorously. 

78.  Combustion  of  illuminating  gas  in  fuming  nitric  acid. 

—  Fuming  nitric  acid,  containing,  as  it  does,  an  excess  of 
the  oxides  of  nitrogen,  supports  the  combustion  of  il- 
luminating gas  even  when  the  end  of  the  tube  conduct- 
ing the  burning  gas  is  thrust  beneath  the  surface  of  the 
acid. 

Fuming  nitric  acid  is  placed  in  a  beaker  in  a  strong  draft. 
A  flame  of  illuminating  gas  about  2  cm.  long  is  allowed  to 
burn  at  the  end  of  a  long  glass  elbow,  and  on  thrusting  the 
burning  flame  under  the  surface  of  the  acid  the  combustion 
will  continue. 

Beaker ;  long  glass  elbow  ;  fuming  HNO3. 


226 


CHEMICAL   LECTURE   EXPERIMENTS 


79.  Decomposition  of  nitric  acid  by  heat.  — At  a  high 
temperature  nitric  acid  undergoes  decomposition,  with  the 
formation  of  nitrogen  peroxide  and  oxygen.  A  very  simple 
and  efficient  method  for  showing  this  decomposition  consists 
in  allowing  the  nitric  acid  in  vapor  form  to  pass  over  pumice- 
stone  heated  in  a  piece  of  combustion  tubing  40  cm.  long 
and  15  mm.  in  diameter,  preferably  of  Jena  glass  (Fig. 
94).  A  thick  piece  of  rubber  tubing  is  slipped  over  one 
arm  of  a  large  glass  elbow  10  mm.  in 
diameter  which  is  then  crowded  into  one 
end  of  the  combustion-tube,  thereby  mak- 
ing a  tight  joint.  In  the  other  end  of 
the   glass  elbow  a  dropping-funnel  con- 


& 


»■ 


Fig.  94 

taining  strong  nitric  acid  is  fitted  by  thrusting  the  stem  of 
the  funnel  through  a  piece  of  rubber  tube  slipped  over  the 
end  of  the  elbow. 

A  roll  of  previously  ignited  asbestos  paper  6  cm.  long  is 
inserted  in  the  combustion-tube  and  so  arranged  that  the 
glass  elbow  is  pushed  a  short  distance  into  its  core.  The 
rest  of  the  tube  is  filled  with  broken  bits  of  pumice-stone 
and  the  end  closed  with  a  cork  carrying  a  small  glass  elbow, 
the  other  end  of  which  is  thrust  some  distance  through  a 
two-holed  rubber  stopper.  The  rubber  stopper  is  inserted 
in  the  mouth  of  a  large  test-tube,  kept  cool  by  being  im- 
mersed in  water,  and  a  delivery-tube  connects  the  test-tube 
with  the  pneumatic  trough.  The  combustion-tube  is  first 
strongly  heated  over  a  four-tube  burner  and  concentrated 


NITRIC   ACID  227 

nitric  acid  then  allowed  to  drop  slowly  (10  to  15  drops  per 
minute)  into  the  glass  elbow.  If  the  tip  of  the  dropping- 
funnel  is  below  the  rubber  connection,  the  rate  of  dropping 
may  be  easily  determined.  The  nitric  acid  flows  down  the 
glass  elbow  and  comes  in  contact  with  the  asbestos  coil. 
This,  acting  as  a  wick,  conducts  the  liquid  toward  the 
warmer  portion  of  the  tube,  where  it  is  gradually  vaporized. 
The  vapor  then  passes  over  the  heated  pumice-stone  and 
there  undergoes  decomposition.  The  water  and  nitrogen 
peroxide  condense  in  the  test-tube  and  the  oxygen  may  be 
collected  at  the  pneumatic  trough.  If  the  burners  are  so 
arranged  that  the  asbestos  roll  is  heated  only  at  one  end,  i.e., 
that  nearest  the  pumice-stone,  by  placing  a  burner  directly 
under  this  end  of  the  asbestos,  a  regular  gradation  of  tem- 
perature is  secured  along  the  asbestos  roll,  which  is  very 
hot  at  the  inner  end  and  cool  at  the  end  nearer  the  cork. 
A  roll  of  wire  gauze  may  be  wound  around  the  outside  of 
that  portion  of  the  combustion-tube  which  is  occupied  by 
the  pumice-stone  and  consequently  requires  the  highest  heat. 
By  use  of  the  asbestos  roll  the  contact  of  the  liquid  with  hot 
glass  is  avoided,  and  the  glass  tube  is  therefore  seldom  broken. 
After  considerable  use  the  rubber  connections  in  each  end 
of  the  combustion-tube  are  destroyed  by  the  action  of  the 
strong  nitric  acid. 

By  allowing  the  acid  to  drop  continually  at  a  very  slow 
rate  the  dropping-funnel  acts  as  a  safety-tube ;  for  should  the 
pressure  inside  the  tube  be  materially  increased,  the  drop- 
ping of  the  acid  would  cease.  The  dropping-funnel  should, 
however,  have  a  constricted  tip  of  not  more  than  3  mm.  in 
diameter,  and  not  more  than  10  cc.  of  acid  should  be  placed 
in  the  dropping-funnel  at  a  time. 

4  HNO3  =  2  H2O  -f  4  KO2  -f  O2. 

Combustion-tubing,  Jena  glass ;  dropping-funnel ;  large  glass  elbow ; 
4-tube  burner  ;  pumice-stone  ;  asbestos  paper  ;  large  test-tube  ;  pneu- 
matic trough  and  cylinders. 


228  CHEMICAL   LECTUBE   EXPERIMENTS 

80.   Test  for  nitric  acid.  —  The  brown  ring  produced  by  the 

action  of  a  solution  of  ferrous  sulphate  on  concentrated  sul- 
phuric acid  containing  nitric  acid    is  strik- 
A  ingly  shown  by  placing  150  cc.  of  sulphuric 

=M  acid  containing  a  small  quantity  of  potassium 

nitrate  in  a  500  cc.  cylinder  and  allowing  a 
concentrated  solution  of  ferrous  sulphate  to 
flow  from  a  dropping-funnel  through  a  glass 
tube  which  delivers  the  liquid  on  the  surface 
of  the  sulphuric  acid  solution  (Fig.  95).  In 
this  way  the  two  liquids  are  introduced,  into 
the  cylinder  without  unnecessary  mixing,  and 
a  deep  brown  ring  is  formed  at  their  surface 
of  contact. 

600  cc.  cylinder  ;  con.  H2SO4  +  KNO3  ;  FeS04  solution. 


HYDRAZINE 

81.   Reducing  action  on  solutions  of  copper  and  silver. — 

Hydrazine  sulphate  is  a  strong  reducing  agent,  causing 
the  reduction  of  alkaline  solutions  of  copper  and  silver 
salts. 

A  solution  of  cupric  sulphate  to  which  tartaric  acid  and 
potassium  hydroxide  have  been  added  is  treated  with  a 
solution  of  hydrazine  sulphate.  Even  in  the  cold  some 
reduction  is  obtained,  and  on  warming  a  little,  cuprous  oxide 
is  precipitated. 

A  solution  of  silver  nitrate  to  which  has  been  added  suf- 
ficient ammonium  hydroxide  to  redissolve  the  precipitate 
first  formed  is  treated  with  a  solution  of  hydrazine  sulphate, 
which,  on  warming,  effects  the  reduction  with  a  deposition 
of  finely  divided  silver. 

Solutions  of  hydrazine  sulphate,  AgNOs,  CUSO4  and  tartaric  acid. 


HYDBAZOIC    ACID  229 

82.  Action  with  potassium  iodate.  —  Hydrazine  sulphate 
reduces  potassium  iodate,  precipitating  iodine,  and  in  the 
process  of  the  reaction  the  hydrazine  is  decomposed,  liber- 
ating nitrogen. 

A  strong  solution  of  potassium  iodate  is  treated  with  a 
solution  of  hydrazine  sulphate.  A  vigorous  evolution  of 
nitrogen  is  obtained,  and  the  mixture  becomes  colored  with 
liberated  iodine.  If  the  two  solutions  are  hot,  the  iodine  is 
vaporized  and  escapes  from  the  mouth  of  the  tube  as  a  violet 
vapor.  A  drop  of  starch  solution  produces  the  characteristic 
blue  color  with  the  iodine. 

15  J^aH^ .  H2SO4  +  12  KIO3  =  15  N2  +  36  HgO  +  6  K2SO4 

+  9H2SO4  +  6I2. 
Hydrazine  sulphate  ;  KIO3  ;  starch  solution. 

83.  Decomposition  of  hydrazine  sulphate  by  heat.  —  Hydra- 
zine sulphate  decomposes  on  heating,  with  the  liberation  of 
sulphur  dioxide,  hydrogen  sulphide,  and  free  sulphur.  A 
few  crystals  of  the  salt  are  heated  in  a  test-tube  and  the 
issuing  gas  tested  for  sulphur  dioxide  and  hydrogen  sul- 
phide. Free  sulphur  will  be  deposited  on  the  sides  of 
the  tube. 

On  dissolving  the  residue  in  water  and  adding  a  few  drops 
of  sulphuric  acid  sulphur  will  be  precipitated. 

HYDRAZOIC  ACID 

84.  Preparation.  —  Nitric  acid,  of  a  specific  gravity  of  1.3, 
when  allowed  to  act  on  hydrazine  sulphate,  gives  a  very 
good  yield  of  hydrazoic  acid. 

One  and  one-half  grams  of  hydrazine  sulphate  are  placed 
in  a  test-tube  fitted  with  a  cork  carrying  a  glass  tube  doubly 
bent  so  as  to  dip  into  a  second  test-tube  containing  silver 


230 


CHEMICAL  LECTURE  EXPERIMENTS 


nitrate  solution  (Fig.  96).  Four  cubic  centimeters  of  nitric 
acid  of  a  specific  gravity  of  1.3  are  added  to  the  hydrazine 
sulphate,  the  cork  inserted,  and  the  mix- 
ture very  slightly  warmed.  As  the  tem- 
perature rises,  the  gas  will  be  evolved  and 
bubble  through  the  silver  nitrate  solution, 
producing  a  curdy  white  precipitate  of 
silver  nitride.  A  piece  of  moistened  lit- 
A  ^     mus  paper,  held  in  the  mouth  of  the  test- 

I  h]     tube  at  the  end  of  the  operation,  shows 

-^    ^     ^     the  acid  character  of  the  gas.     The  silver 
Fig.  96  nitride  formed  should  be  filtered  off,  thor- 

oughly washed  with  water,  and  allowed 
to  stand  till  ready  for  use  in  the  following  experiments. 
Owing  to  its  dangerously  explosive  nature  but  small  quanti- 
ties must  be  dried  at  a  time. 

Hydrazine  sulphate  ;  HNO3  (1.3  specific  gravity)  ;  AgNOs  solution. 

85.  Preparation  of  hydrazoic  acid  (silver  nitride)  from 
hydrazine  sulphate  and  silver  nitrite.  —  Silver  nitrite  reacts 
with  a  solution  of  hydrazine  sulphate,  forming  silver  nitride. 

Twenty-five  cubic  centimeters  of  a  saturated  solution  of 
hydrazine  sulphate  in  water  are  placed  in  a  50  cc.  flask  to 
which  silver  nitrite  in  small  quantities  is  gradually  added. 
The  reaction  is  quite  marked,  the  white,  curdy  silver  nitride 
remaining  suspended  in  the  liquid.  The  precipitate  should 
be  filtered  and  dried  as  above.  But  very  small  quantities 
should  be  prepared  at  one  time. 

N2H,  +  AgNO,  =  AgN3  +  2H2O. 

Hydrazine  sulphate ;  AgNOg. 

86.  Explosive  nature  of  silver  nitride.  —  The  great  explosi- 
bility  of  silver  nitride  necessitates  that  experiments  on  this 
compound  be  carried  out  on  a  very  small  scale  only.     A 


HYDRAZOIC   ACID  231 

minute  quantity  (2  or  3  mg.)  is  heated  on  a  knife-blade 
thrust  into  the  Bunsen  burner.     The  explosion  is  very  great. 

If  a  minute  quantity  of  the  precipitate  is  placed  in  the 
centre  of  a  thin  copper  sheet  which  is  then  suddenly  thrust 
into  the  flame,  the  force  of  the  explosion  is  such  as  to  make 
a  dent  in  the  copper. 

Silver  nitride  is  equally  sensitive  to  friction,  and  a  small 
piece  placed  between  paper  on  an  anvil  and  struck  with  a 
hammer  detonates  with  great  violence. 

Hammer  and  anvil;  dry  AgNs  (Care  ! ! !);  thin  sheet  copper. 


PHOSPHORUS 


PHOSPHORUS 


MANIPULATION 


1.  Precautions  in  handling  phosphorus.  —  Owing  to  its 
inflaminable  nature  and  the  dangerous  character  of  the 
wounds  resulting  from  its  burns,  phosphorus  must  be  han- 
dled with  the  greatest  care.  It  may  be  handled  beneath 
water  with  perfect  impunity,  though  too  much  care  cannot 
be  exercised  in  avoiding  danger  from  particles  adhering  to 
the  fingers  and  finger  nails.  In  all  operations  where  phos- 
phorus is  to  be  removed  from  the  water  it  should  never  be 
touched  with  the  naked  fingers,  but  with  pincers  or  crucible 
tongs.  Small  pieces  can  be  cut  from  a  piece  of  phosphorus 
by  submerging  the  knife  and  hand  as  well  as  the  phosphorus 
in  water.  A  more  satisfactory  method  of  obtaining  small 
pieces  is  to  use  the  globules  as  prepared  in  Ex.  4,  or  to  break 
off  pieces  of  the  desired  length  from  sticks  of  small  calibre 
prepared  as  in  Ex.  3.  In  drying  a  piece  of  phosphorus 
between  filter-paper  the  greater  portion  of  the  water  should 
be  allowed  to  drain  off  by  capillary  attraction,  and  then  the 
paper  should  be  folded  once  over  the  phosphorus  and  gently 
pressed  with  the  fingers.  Under  no  circumstances  should 
the  fingers  come  in  direct  contact  with  the  phosphorus.  In 
cutting   phosphorus  it  is  important   that  the   vessel   used 


PHOSPHORUS 


^33 


should  be  thick,  so  as  not  to  be  broken  by  the  accidental 
slipping  of  the  knife. 

Phosphorus  is  always  kept  under  water,  and  care  should 
be  taken  that  the  phosphorus  after  long  standing  does  not 
become  uncovered  by  the  evaporation  of  the  water  in  the 
vessel. 

Wounds  resulting  from  burns  of  phosphorus  demand  spe- 
cial and  immediate  treatment.  They  are  very  persistent 
and  slow  to  heal,  often  resulting  in  running  sores  of  a  seri- 
ous nature.  The  burn  should  immediately  be  washed  in 
water  and  moistened  with  sodium  bicarbonate  or  a  dilute 
solution  of  bleaching-powder. 

Burning  phosphorus  should  be  extinguished  as  directed 
in  Ex.  8. 


2.  Melting  and  casting  phosphorus.  —  Commercial  phos- 
phorus is  ordinarily  obtained  in  the  form  of  sticks.  Since 
after  keeping  for  some  time,  especially  on  exposure  to  the 
light,  the  phosphorus  acquires  a  dark  color,  it  is  desirable  to 
show  the  translucent,  waxy  appearance  of  pure  phosphorus 
by  melting  the  commercial  material  and 
recasting  it  in  sticks  of  convenient  size. 

Several  sticks  of  phosphorus  are  placed 
in  a  beaker  and  completely  covered 
with  water.  The  beaker  is  then  placed 
in  an  evaporating-dish  partially  filled 
with   water,    which 

is  brought  nearly  to    '^ ^^^ 

the    boiling    point. 

As     the    water    in 

the  beaker  becomes 

warm,  the  phosphorus  melts  and  settles  to  the  bottom  of 

the  beaker.     The  phosphorus  is  best  cast  in  small  thin-glass 

test-tubes,  which  are  tilled  with  water  and  immersed  in  a 


^^ 


Fig.  97 


Fig.  98 


234 


CHEMICAL  LECTURE  EXPERIMENTS 


large  beaker  of  warm  water.  If  the  beaker  in  which  the 
phosphorus  has  been  melted  is  small  enough,  it  also  may  be 
immersed  in  the  water  in  the  large  beaker  and  the  phos- 
phorus poured  under  water  into  the  test-tubes  (Fig.  98). 
It  is  necessary  to  leave  a  centimeter  layer  of  water  on  top 
of  the  phosphorus  in  each  test-tube. 

The  molten  phosphorus  may  be  drawn  up  into  a  pipette 
and  then  allowed  to  run  into  the  test-tubes.  A  25  cc.  pipette 
with  a  rather  wide  delivery-tip  is  immersed  in  a  tall  cyl- 
inder filled  with  warm  water  (Fig.  99). 
The  pipette  is  then  withdrawn,  allowing 
the  water  to  flow  out,  and  while  still 
warm  dipped  into  the  beaker  containing 
the  melted  phosphorus.  A  layer  of  water 
is  first  drawn  into  the  pipette  and  then 
the  end  dipped  beneath  the  molten  phos- 
phorus. The  pipette  is  nearly  filled  with 
phosphorus  and  then  transferred  to  the 
beaker  holding  the  test-tubes.  As  in  this 
transference  a  few  drops  of  melted  phos- 
phorus are  liable  to  fall  out  of  the  tip  of 
the  pipette,  it  is  best  to  seal  the  tip  by 
dipping  it  into  a  deflagrating-spoon  filled 
with  water.  The  pipette  should  occasion- 
ally be  dipped  in  the  water  in  the  tall 
cylinder  to  keep  it  warm  enough  to  prevent  the  phosphorus 
from  solidifying.  After  a  few  test-tubes  are  filled  they  may 
be  removed  from  the  beaker  and  placed  in  a  test-tube  rack, 
the  layer  of  water  on  top  preventing  oxidation.  After  a  few 
minutes  the  contents  of  the  tubes  will  have  solidified,  and  by 
making  a  hole  in  the  bottom  of  each  tube  the  stick  of  phos- 
phorus may  be  forced  out  under  water.  Made  in  this  man- 
ner, the  sticks  show  the  true  color  of  the  yellow  phosphorus, 
and  should  be  preserved  under  water  in  the  dark.     If  care  is 


" 

"^I? 

= 

ri:: 

— 

<::,:           ^ 

Fig.  99 


PHOSPHORUS  235 

always  taken  to  draw  a  little  water  into  the  pipette  before 
the  phosphorus  and  to  keep  the  tip  of  the  pipette  always 
under  the  phosphorus  or  water,  the  suction  may  be  applied 
with  the  mouth,  though  it  should  always  be  borne  in  mind 
that  carelessness  will  result  in  drawing  melted  phosphorus 
into  the  mouth.  A  safer  method  of  operating  is  to  insert  a 
gas  washing-bottle  containing  a  small  amount  of  water  be- 
tween the  mouth  and  the  pipette.  The  air  should  be  drawn 
through  the  glass  tube  whose  end  terminates  just  below  the 
cork.  If  any  phosphorus  should  accidentally  be  drawn  over, 
it  would  pass  through  the  long  tube  extending  to  the  bottom 
of  the  bottle,  and  there  be  delivered  under  water. 

Large  evaporating-dish  ;  tall  cylinder ;  gas  washing-bottle ;  25  cc. 
pipette  ;  deflagrating-spoon  ;  thin  test-tubes  ;  P. 

3.  Preparation  of  stick  phosphorus. — Phosphorus  may 
also  be  obtained  in  the  stick  form  by  drawing  the  molten 
liquid  up  into  a  glass  tube  of  the  diameter  of  the  sticks 
desired. 

A  glass  tube,  from  8  to  10  mm.  internal  diameter  and  20 
cm.  long,  is  provided  with  a  one-holed  cork  or  rubber  connec- 
tion which  is  attached  to  a  gas  washing-bottle  as  described 
in  the  preceding  experiment.  The  tube  is  dipped  beneath 
the  surface  of  the  molten  phosphorus  under  water  in  a  beaker, 
and  by  means  of  gentle  suction  a  column  of  the  liquid  some 
10  cm.  long  is  drawn  into  the  tube.  The  lower  end  of  the 
tube  is  then  sealed  with  a  small  deflagrating-spoon  filled 
with  water  atid  the  tube  immersed  in  a  beaker  of  cold  water. 
In  a  few  moments  the  phosphorus  will  have  solidified  and,  by 
removing  the  rubber  tube,  the  stick  may  be  forced  out  under 
water  with  a  glass  rod.  By  selecting  tubes  of  different  sizes 
it  is  easy  to  obtain  rods  of  phosphorus  of  any  size  desired. 
A  rubber  tube  should  connect  the  gas  washing-bottle  with 
the  mouth,  and  a  pinch-cock  may  be  advantageously  employed 


236  CHEMICAL   LECTURE   EXPERIMENTS 

to  close  the  tube  after  the  phosphorus  has  been  drawn  up. 
In  using  a  deflagrating-spoon  to  seal  the  end  of  the  tube  it  is 
essential  that  a  layer  of  water  should  remain  in  the  spoon 
when  it  is  withdrawn  into  the  air,  as  otherwise  the  phos- 
phorus may  easily  become  ignited. 

Glass  tubes  of  different  sizes ;  gas  washing-bottle  ;  deflagrating- 
spoon  ;  P. 

4.  Preparation  of  globules  of  phosphorus.  —  In  the  greater 
number  of  experiments  in  which  phosphorus  is  used  the 
amount  required  is  exceedingly  small,  and  consequently  it  is 
necessary  either  to  cut  off  small  pieces  of  phosphorus  from 
a  large  stick  or  to  subdivide  the  molten  phos- 
phorus in  such  a  manner  that  it  may  solidify  in 
small  globules.  This  latter  operation  is  easily 
performed  by  allowing  molten  phosphorus  to 
flow  out  of  a  jet  down  through  a  column  of  ice- 
cold  water. 

A  25  cc.  pipette  is  filled  with  phosphorus,  as 
described  in  Ex.  4,  and  its  tip  thrust  just  be- 
neath the  surface  of  water  in  a  tall  cylinder. 
The  cylinder  is  nearly  filled  with  ice-water  and 
then  a  2  cm.  layer  of  warm  water  carefully 
poured  on  top.  The  layer  of  warm  water  pre- 
vents the  solidifying  of  phosphorus  in  the  tip  of 
the  pipette.  The  phosphorus  is  then  allowed 
to  trickle  slowly  out  of  the  pipette  and  fall 
through  the  long  column  of  ice-cold  water. 
During  its  passage  the  globules  solidify  and  collect  in 
small  beads  at  the  bottom  of  the  cylinder.  By  varying 
the  size  of  the  tip  of  the  pipette  and  regulating  the  flow 
of  the  phosphorus,  larger  or  smaller  globules  can  be  ob- 
tained. The  glass  cylinder  should  be  at  least  40  cm.  high 
(Fig.  100). 


PHOSPHORUS  237 

Minute  globules,  which  are  often  advantageous  for  oper- 
ating with  phosphorus,  may  be  obtained  by  melting  a  few 
grams  of  phosphorus  under  25  cc.  of  water  in  a  100  cc.  flask. 
When  the  phosphorus  is  melted,  the  flask  is  tightly  corked 
and  the  contents  well  shaken.  The  phosphorus  solidifies  in 
very  fine  globules,  which  should  be  kept  under  water  in  a 
tightly  corked  bottle. 

25  cc.  pipette  ;  cylinder  40  cm.  high  ;  P. 

5.  Purification  of  phosphorus.  —  Ordinary  phosphorus  may 
be  purified  and  deprived  of  its  dark-colored  coating  by  melt- 
ing it  under  a  dilute  solution  of  potassium  dichromate  and 
sulphuric  acid. 

The  acid  mixture  and  phosphorus  should  be  placed  in  a 
beaker,  which  is  in  turn  partly  immersed  in  hot  water  in  an 
evaporating-dish  or  water-bath.  The  phosphorus  soon  melts 
and,  at  the  end  of  15  minutes,  the  impurities  will  have  been 
so  far  dissolved  as  to  leave  the  phosphorus  a  clear,  almost 
colorless  liquid  in  the  bottom  of  the  beaker.  The  oxidizing 
mixture  may  be  washed  from  the  beaker  by  decantation  and 
the  purified  phosphorus  cast  into  sticks  as  described  in  Ex.  2. 

Water-bath  ;  beaker  ;  yellow  P  ;  K2Cr207. 

PROPERTIES 

6.  Spontaneous  inflammability.  —  Phosphorus  at  the  ordi- 
nary temperatures  is  energetically  oxidized  by  the  oxygen  of 
the  air  and  is  often  spontaneously  ignited.  A  clean  piece  of 
phosphorus,  if  allowed  to  stand  exposed  to  the  air  in  a  warm 
room,  will  oxidize  and  ultimately  ignite.  To  show  the  spon- 
taneous inflammability  of  phosphorus  it  is  necessary  to  have 
the  phosphorus  finely  divided.  The  fine  globules  of  phos- 
phorus prepared  in  Ex.  4,  if  dried  on  filter-paper  and  ex- 
posed to  the  air,  will  oxidize  more  rapidly  than  a  large 
piece,  and  the  subdivision  obtained  by  the  evaporation  of  a 


238  CHEMICAL  LECTURE   EXPERIMENTS 

solution  of  phosphorus  in  carbon  disulphide  leaves  a  residue 
of  phosphorus  so  finely  subdivided  as  to  ignite  immediately. 

Phosphorus  is  very  easily  soluble  in  earbon  disulphide,  and 
a  solution  may  be  prepared  by  dissolving  a  7  mm.  piece  of 
dry  phosphorus  in  5  cc.  of  carbon  disulphide  in  a  test-tube. 
A  piece  of  filter-paper  dipped  in  the  solution  and  exposed 
to  the  air  will  soon  take  fire ;  for  as  the  carbon  disulphide 
evaporates,  the  dissolved  phosphorus  is  deposited  all  over 
the  fibre  of  the  paper,  and  in  this  finely  divided  condition 
is  rapidly  oxidized  in  the  air.  Owing  to  the  non-volatile 
nature  of  the  phosphorus  pentoxide  formed,  the  paper  itself 
is  not  burned,  but  only  partially  charred. 

As  the  paper  is  not  ignited  under  these  circumstances,  a 
letter  or  design  may  be  drawn  on  the  paper  with  a  camePs- 
hair  brush  dipped  in  the  solution  of  phosphorus.  On  evap- 
oration of  the  carbon  disulphide  the  phosphorus  is  ignited 
and  chars  the  design  on  the  paper. 

The  luminosity  of  the  oxidizing  phosphorus  is  well  shown 
in  a  darkened  room  by  drawing  a  design  with  the  liquid  on 
a  board.  As  the  carbon  disulphide  evaporates  and  the  phos- 
phorus is  oxidized,  the  design  appears  in  lines  of  fire. 

Camel's-hair  brush;  CS2  solution  of  P. 

7.  Spontaneous  combustion  effected  by  powdered  charcoal. 

—  A  piece  of  well-dried  phosphorus,  when  placed  on  a  filter- 
paper  and  covered  with  powdered  charcoal,  is  ignited.  The 
action  requires  some  little  time,  but  owing  to  the  gases  con- 
densed in  the  charcoal  as  well  as  its  non-conductivity  for 
heat,  the  temperature  within  the  mass  ultimately  reaches 
the  ignition  point  of  phosphorus. 

8.  Extinguishing  a  flame  of  burning  phosphorus.  —  Burn- 
ing phosphorus  is  difficult  to  extinguish  by  the  addition  of 
water. 


PHOSPHORUS  239 

A  piece  of  clean,  dry  phosphorus  is  placed  in  a  small  tin 
saucer  (the  cover  to  a  baking-powder  can)  or  iron  sand-bath, 
and  ignited.  When  the  phosphorus  is  burning  well,  a  few 
centimeters  of  water  are  added  from  a  test-tube,  and  it  will 
be  seen  that  the  phosphorus,  melted  by  the  heat,  will  par- 
tially float  and  continue  to  burn  and  sputter  in  the  dish. 
A  similar  piece  of  phosphorus  placed  on  an  iron  plate  and 
ignited  is,  however,  readily  extinguished  by  covering  it  with 
sand.  In  experimenting  with  phosphorus  it  is  advisable 
to  have  a  beaker  full  of  sand  within  easy  reach.  After  the 
phosphorus  is  extinguished  some  care  is  necessary  to  remove 
the  sand  and  extinguished  phosphorus  without  accident,  and 
hence  it  is  often  advisable  to  allow  small  pieces  of  phos- 
phorus to  "burn  out,"  exercising  care  that  no  damage  is 
done. 

Tin  saucer ;  iron  plate  ;  sand  ;  gauntlets ;  P. 

9.  Combustion  on  cotton.  —  Phosphorus  pentoxide,  the 
product  of  the  combustion  of  phosphorus  in  air,  is  volatilized 
with  difficulty,  and  hence  forms  a  protective  coating  to  com- 
bustible material,  when  phosphorus  is  burned  in  contact 
with  it.  This  was  seen  in  Ex.  6,  where  the  coating  of 
phosphorus  pentoxide  prevented  the  combustion  of  filter- 
paper. 

The  experiment  may  be  carried  out  on  a  larger  scale  by 
placing  an  8  mm.  piece  of  dry  phosphorus  in  a  little  depres- 
sion made  in  a  large  wad  of  cotton  batting.  On  igniting 
the  phosphorus  it  burns  quietly,  and  the  cotton  fibres  in  the 
immediate  vicinity  of  the  burning  phosphorus  become  some- 
what charred.  It  will  be  found,  however,  on  examining 
the  piece  of  cotton,  after  the  complete  combustion  of  the 
phosphorus,  that  the  flame  has  not  been  communicated  to 
the  fibre. 

Wad  of  cotton  batting  ;  8  mm.  piece  of  dry  P. 


240 


CHEMICAL   LECTURE    EXPERIMENTS 


10.  Combustion  under  water.  —  When  a  stream  of  oxygen 
is  conducted  through  melted  phosphorus,  the  phosphorus 
burns,  combining  with  the  oxygen  even  under  water. 

A  few  grams  of  phosphorus  are  melted  under  water  in  a 
large  test-tube,  which  in  turn  is  half  immersed  in  a  beaker 
of  water  warmed  to  80°.  A  gentle  stream  of  oxygen  is  con- 
ducted through  a  piece  of  clay  pipe- 
stem,  which  is  inserted  in  the  test-tube 
(Fig.  101).  As  the  oxygen  comes  in 
contact  with  the  melted  phosphorus,  it 
burns  brilliantly,  forming  phosphorus 
'*"  pentoxide,  which  unites  with  the  water 
above  the  phosphorus  to  form  phos- 
phoric acid.  A  portion  of  the  phos- 
phorus becomes  converted  by  the  heat 
of  the  combustion  into  the  red  modifi- 
cation, which  remains  suspended  in  the 
liquid.  It  will  be  found  that  when  the 
initial  temperature  of  the  phosphorus 
and  water  is  as  low  as  60°,  combustion 
will  take  place,  though,  owing  to  the 
heat  of  the  combustion  of  the  phosphorus,  the  water  is 
soon  warmed  above  this  temperature.  The  water  above 
the  phosphorus  will  be  found  to  have  an  intensely  acid 
reaction  at  the  end  of  the  combustion. 

P,  +  502  =  2PA. 
3H20  +  PA  =  2H3P04. 

Apparatus  (Fig.  101)  ;  clay  pipe-stem  ;  O  supply;  P. 


E^ 


^ 


Fig.  101 


11.  Vaporization  in  a  current  of  steam.  —  (a)  Phosphorus 
in  the  presence  of  steam  is  rapidly  volatilized,  and  the  re- 
action of  this  vapor  on  a  paper  moistened  with  silver  nitrate 


PHOSPHORUS  241 

solution  furnishes  a  delicate  test  for  the  presence  of  free 
phosphorus. 

A  phosphorus  match  head  is  covered  with  20  cc.  of  boiling 
water  in  a  500  cc.  flask.  After  a  few  moments  the  water  is 
poured  out,  leaving  the  match  head  in  the  flask.  A  piece 
of  filter-paper  moistened  with  silver  nitrate  solution  is  fas- 
tened to  a  wire  in  a  cork  and  lowered  into  the  flask.  In 
the  course  of  a  few  minutes  the  paper  becomes  brownish 
in  color  and  finally  black  from  the  formation  of  silver 
phosphide. 

A  paper  moistened  with  lead  acetate  solution,  suspended 
in  the  flask  at  the  same  time,  proves  that  the  blackening 
cannot  be  due  to  the  formation  of  hydrogen  sulphide,  as  the 
lead  acetate  paper  remains  unchanged.       *■ 

500  cc.  flask  ;  solutions  of  AgNOa,  Pb(C2H302)2. 

(b)  The  phosphorescence  of  a  current  of  steam  containing 
phosphorus  vapor  is  readily  obtained  by  heating  the  head  of 
a  phosphorus  match  with  20  cc.  of  water  in  a  100  cc.  flask 
provided  with  a  cork  carrying  a  short  piece  of  glass  tubing 
(6  mm.  internal  diameter).  On  bringing  the  water  to  a  boil 
steam  will  escape  from  the  glass  tube,  and  in  a  darkened 
room  the  jet  will  be  found  to  be  feebly  luminous  from  the 
oxidation  of  the  phosphorus  vapor. 

12.  Phosphorus  colors  the  hydrogen  flame  green.  — One  of 

the  most  delicate  tests  for  the  presence  of  free  phosphorus 
is  based  on  the  fact  that  phosphorus  tints  the  colorless 
hydrogen  flame  green. 

A  hydrogen  generator  is  constructed  by  inserting  a  straight 
glass  tube  7  mm.  in  diameter  through  a  two-holed  rubber 
stopper  in  a  small  Erlenmeyer  flask  (Fig  102).  The  second 
hole  carries  a  glass  tube  so  bent  as  to  form  a  jet,  and  a 
platinum  tip  such  as  that  described  in  Ex.  5,  p.  183,  should 

B 


242 


CHEMICAL  LECTURE   EXPERIMENTS 


be  inserted  in  the  glass  tube.  A  few  pieces  of  zinc  are 
placed  in  the  bottom  of  the  flask  and  covered  with  water. 
The  wide  glass  tube  should  extend  to  within 
5  mm.  of  the  bottom  of  the  flask,  and  serves 
to  introduce  sufficient  sulphuric  acid  to  start 
the  generation  of  hydrogen.  After  the  addi- 
tion of  acid  the  flask  should  be  shaken,  and, 
as  soon  as  all  air  is  driven  out,  the  hydro- 
gen is  lighted  at  the  platinum  tip.  A  phos- 
phorus match  head  is  softened  in  hot  water 
for  a  few  moments,  and  then  dropped  through 
the  wide  glass  tube  into  the  generator.  The 
hydrogen  flame,  which  was  colorless,  is  soon 
colored  green  from  the  phosphorus  of  the 
match  head. 


Fig.  102 


150  cc.  Erlenmeyer  flask ;  glass  tube  (7  mm.  diameter)  ;  platinum 


jet. 


f 


13.  Action  of  fuming  nitric  acid.  —  At  times  fuming  nitric 
acid  oxidizes  phosphorus  to  phosphoric  acid  with  almost  ex- 
plosive violence.  The  commercial  method 
of  preparing  phosphoric  acid  depends  on 
this  reaction,  and  its  regulation  is  there- 
fore a  matter  of  considerable  importance. 

A  crucible  one-third  filled  with  fuming 
nitric  acid  is  imbedded  in  a  layer  of  sand 
at  the  bottom  of  a  tall  glass  beaker  or 
cylinder  (Fig.  103),  which  is  placed  in  the 
hood.  A  7  mm.  piece  of  dried  phosphorus 
impaled  on  the  end  of  a  long  iron  wire, 
bent  in  such  a  manner  as  to  be  easily 
thrust  into  the  cylinder,  is  brought  in 
contact  with  the  fuming  nitric  acid  in  the  crucible, 
a  few  moments  the  phosphorus  bursts  into  flame. 


Fig.  103 


After 
When 


PHOSPHORUS  243 

the  combustion  is  completed,  the  crucible  may  be  carefully 
removed  with  the  gloved  hand,  and  the  contents  diluted 
with  water.     The  liquid  contains  phosphoric  acid. 

Crucible  ;  cylinder  with  sand  ;  iron  wire  ;  gauntlets  ;  fuming  HNOg  ; 
yellow  phosphorus. 

14.  Action  on  potassium  chlorate.  —  Phosphorus  and  po- 
tassium chlorate  form  a  violently  explosive  mixture,  which 
must  be  handled  on  a  very  small  scale  only. 

A  very  intimate  mixture  of  phosphorus  and  potassium 
chlorate  is  obtained  by  allowing  1  or  2  drops  of  a  strong 
solution  of  phosphorus  in  carbon  disulphide  to  fall  from  a 
dry  test-tube  upon  a  very  small  heap  of  finely  powdered 
potassium  chlorate  placed  on  a  brick  or  a  piece  of  asbestos 
paper.  The  carbon  disulphide  soon  evaporates,  leaving  a 
fine  deposit  of  phosphorus  all  through  the  finely  powdered 
potassium  chlorate.  As  soon  as  the  phosphorus  ignites,  the 
combustion  proceeds  through  the  whole  mass  with  a  very 
sharp  explosion. 

Powdered  KCIO3  ;  CS2  solution  of  P. 

15.  Effect  of  pure  oxygen  on  the  glowing  of  phosphorus.  — 

A  stick  of  phosphorus,  suspended  by  a  thread,  glows  in  a 
darkened  room,  but  if  lowered  into  a  jar  of  oxygen,  the  glow- 
ing ceases. 

The  experiment  may  be  varied  by  placing  the  phosphorus 
in  a  cylinder  containing  air,  where  it  glows  as  usual.  On 
conducting  oxygen  into  the  cylinder  the  glowing  ceases. 

Cylinder  of  O  ;  stick  of  P. 

16.  Glowing  in  oxygen   under   diminished    pressure. — 

While  phosphorus  will  not  glow  in  pure  oxygen  at  atmos- 
pheric pressure,  if  the  oxygen  is  partially  removed  from  the 
vessel,  the  phosphorus  will  glow  in  the  rarefied  gas. 


244  CHEMICAL   LECTURE    EXPERIMENTS 

A  stick  of  phosphorus  is  lowered  into  a  tall,  narrow  cylin-; 
der  of  oxygen  fitted  with  a  one-holed  rubber  stopper  carryiiig 
a  glass  elbow.  The  elbow  is  connected  with  a  filter-pump. 
The  phosphorus  will  not  glow  in  the  cylinder  of  oxygen,  but 
as  soon  as  the  filter-pump  is  started  the  glowing  begins. 
On  allowing  oxygen  to  enter  again  the  glow  ceases.  Advan- 
tageous use  may  here  be  made  of  a  three-way  stop-cock,  one 
arm  of  which  is  inserted  in  the  rubber  stopper,  the  other  arm 
connected  with  an  oxygen  supply,  and  the  stem  connected 
with  the  filter-pump.  The  three-way  cock  may  be  so  turned 
as  to  connect  with  the  filter-pump  to  produce  the  desired 
diminished  pressure.  By  turning  the  cock  again  oxygen 
may  be  readmitted. 

Tall,  narrow  cylinder ;  filter-pump  ;  three-way  cock  ;  O  supply  ; 
stick  of  P. 

17.   Action  of  vapors  on  the  glowing  of  phosphorus.  — (a) 

A  stick  of  phosphorus  placed  in  a  glass  cylinder  and  ex- 
posed to  the  air  glows  in  a  darkened  room.  On  allowing 
2  or  3  drops  of  ether  to  fall  into  the  cylinder  the  glowing 
immediately  ceases.  On  withdrawing  the  phosphorus  into 
the  air  the  glowing  reappears.  Turpentine  or  carbon  di- 
sulphide  instead  of  ether  may  be  used  with  similar  effect. 

Stick  phosphorus  ;  ether  ;  CS2 ;  turpentine. 

(6)  The  fact  that  phosphorus  will  not  glow  in  oxygen 
containing  traces  of  certain  other  vapors  is  well  shown  by 
lowering  into  a  jar  of  oxygen  a  piece  of  filter-paper  on  which 
a  few  drops  of  a  solution  of  phosphorus  in  carbon  disulphide 
have  been  placed.  A  cardboard  cover  should  be  laid  over 
the  mouth  of  the  jar.  A  similar  piece  of  paper  when  held 
in  the  air  is  ignited  in  a  few  moments,  while  that  in  the 
atmosphere  of  oxygen  is  not.  On  withdrawing  the  paper 
into  the  air  it  almost  instantly  catches  fire. 

Jar  of  O  ;  cardboard  cover  ;  CS2  solution  of  P. 


AMOKPHOUS  PHOSPHORUS  245 

18.  Reduction  of  metallic  salt  solutions.  —  Phosphorus  is  a 
strong  reducing  ageut,  and  precipitates  many  metals  from 
their  solutions. 

(a)  Cupric  sulphate.  A  stick  of  clean  phosphorus  is 
immersed  in  a  solution  of  cupric  sulphate  which  is  strong 
enough  to  appear  decidedly  blue.  After  a  few  minutes  the 
phosphorus  will  become  covered  with  a  coating  which  con- 
sists of  copper  mixed  with  some  copper  phosphide.  If  the 
phosphorus  is  allowed  to  remain  in  the  solution  till  the  next 
exercise,  all  of  the  copper  will  be  removed  from  the  solution, 
and  the  clear  colorless  solution  will  give  no  test  for  copper 
when  ammonium  hydroxide  is  added  to  it. 

Concentrated  CUSO4  solution  ;  stick  of  P. 

(b)  Silver  nitrate.  A  piece  of  clean  phosphorus,  when  im- 
mersed in  a  solution  of  silver  nitrate,  becomes  covered  with 
a  metallic,  crystalline  coating  of  a  mixture  of  silver  and 
silver  phosphide. 

AgNOs  sokition  ;  stick  of  P. 

(c)  Gold  chloride.  A  piece  of  clean  phosphorus  im- 
mersed in  a  rather  strong  solution  of  gold  chloride  is  imme- 
diately coated  with  a  deposit  of  gold,  which,  owing  to  its 
fine  subdivision,  appears  black. 

AuClg  solution  ;  stick  of  P. 

AMORPHOUS   PHOSPHORUS 
(RED  PHOSPHORUS) 

FORMATION   AND   PREPARATION 

19.  By  the  combustion  of  ordinary  phosphorus.  —  Ordinary 
yellow  phosphorus,  when  burned  in  the  air,  is  partially  con- 
verted into  the  allotropic  form  known  as  red  phosphorus. 
In  Ex.  4,  p.  182,  where  phosphorus  is  burned  in  a  con- 


246  CHEMICAL   LECTUBB  EXPERIMENTS 

fined  volume  of  air,  considerable  quantities  of  red  phosphorus 
will  be  found  remaining  in  the  crucible  lid. 

20.  By  the  action  of  light  on  yellow  phosphorus.  —  Pure 
yellow  phosphorus  always  turns  dark  on  exposure  to  the 
light,  hence  it  is  recommended  to  keep  the  purified  phos- 
phorus in  a  dark  place. 

The  change  in  color  undergone  by  exposure  to  the  light  is 
very  markedly  shown  by  exposing  to  the  sunlight  for  a  few 
hours  a  tightly  corked  test-tube  containing  a  stick  of  pure 
phosphorus,  which  is  covered  with  water.  In  the  course  of 
a  day  of  bright  sunlight  the  phosphorus  will  have  materially 
reddened,  as  may  be  seen  by  comparing  the  exposed  piece 
with  a  fresh  piece  of  pure  phosphorus.  The  color  change  is 
still  more  noticeable  if  the  lower  half  of  the  test-tube  is 
wrapped  with  black  paper  which  cuts  off  the  light  from  the 
lower  half  of  the  stick  of  phosphorus.  If  such  a  piece  is 
exposed  to  the  sunlight,  the  upper  half  will  turn  a  dark  red, 
while  the  lower  part  remains  unchanged. 

Black  paper ;  freshly  prepared  stick  P. 

21.  By  the  action  of  iodine.  —  A  5  mm.  piece  of  well- 
dried  yellow  phosphorus  is  heated  to  boiling  in  a  test-tube. 
Very  little,  if  any,  change  in  color  will  be  obtained.  On 
adding  a  minute  crystal  of  iodine  and  reheating,  the  whole 
mass  becomes  converted  to  red  phosphorus. 

Yellow  P ;  I. 

PROPERTIES 

22.  Conversion   to   yellow    phosphorus   by    heat.  —  Eed 

phosphorus,  when  heated  at  a  high  temperature,  becomes 
converted  to  yellow  phosphorus. 

An  8  cm.  length  of  small  glass  tubing  is  sealed  at  one  end 
and  a  quantity  of  red  phosphorus  introduced  into  the  tube. 


AMORPHOUS  PHOSPHORUS 


247 


On  heating  the  phosphorus  a  gas  escapes,  which  is  spontane- 
ously inflammable,  the  impure  hydrogen  phosphide  resulting 
from  the  decomposition  of  a  small  amount  of  phosphorous 
acid  in  the  red  phosphorus.  As  the  heat  is  increased,  yellow 
phosphorus  is  formed  and  condenses  in  oily  drops  in  the 
upper  part  of  the  tube. 

Red  phosphorus  contains  an  appreciable  quantity  of  phos- 
phorous acid,  and  if  water  is  allowed  to  pass  through  it  on  a 
filter-paper  the  filtrate  will  be  decidedly  acid  to  litmus. 

8  cm.  length  small  glass  tubing  ;  red  P  ;  litmus. 

23.  Difference  in  the  ignition  point  of  the  two  modifica- 
tions of  phosphorus.  —  The  ignition  point  of  red  phosphorus 
is  very  much  higher  than  that  of  yellow  phosphorus.  This 
difference  may  be  shown  by  placing  a  small  quantity  of  yel- 
low phosphorus  on  the  end  of  an  iron  bar  about  15  cm.  long. 
A  small  heap  of  red  phosphorus  is  placed  on  the  other  end. 
The  bar  is  then  suspended  on  the  ring  of  a  retort  stand  and 
heated  in  the  middle  with  a  Bunsen  burner.  After  a  few 
moments  the  yellow  phosphorus  will  ignite,  but  it  will  re- 
quire considerable  time  and  a  much  higher 
heat  to  cause  the  ignition  of  the  red  phos- 
phorus. 

The  experiment  may  be  varied  some- 
what by  placing  the  yellow  phosphorus  at 
a  greater  distance  from  the  flame  than  the  — 
red.  For  this  purpose  a  strip  of  brass, 
some  20  cm.  long  and  2.5  cm.  wide,  is 
clamped  at  one  end  in  a  horizontal  posi- 
tion (Fig.  104).  A  small  heap  of  red  phos-  ^~- 
phorus  is  placed  at  a  point  about  4  cm.  fig.  104 

from  the  free  end  and  a  small  piece  of  yel- 
low phosphorus  is  placed  at  a  distance  of  10  cm.  from  the 
red.     The  end  of  the  brass  is  then  heated  with  a  Bunsen 


:2^ 


248       CHEMICAL  LECTURE  EXPERIMENTS 

burner.  In  a  few  moments  sufficient  heat  will  have  been 
conducted  along  the  strip  of  brass  to  ignite  the  yellow  phos- 
phorus, while  the  red  phosphorus,  which  is  nearer  the  flame, 
remains  unchanged.  On  increasing  the  heat  somewhat  the 
red  phosphorus  will  finally  be  ignited. 

Iron  bar  (15  cm,  long)  ;  brass  strip  20  cm.  by  2.5  era. ;  red  P  ;  yel- 
low P. 

24.  Combustion  in  air.  —  That  the  product  obtained  by 
burning  red  phosphorus  in  the  air  is  the  same  as  that  ob- 
tained by  burning  yellow  phosphorus,  is  an  indication  of  the 
chemical  identity  of  these  two  forms  of  the  element. 

A  small  quantity  of  red  phosphorus  is  placed  in  a  crucible 
on  a  plate  and  covered  with  a  bell-jar.  On  igniting  the 
phosphorus  the  combustion  proceeds  as  with  yellow  phos- 
phorus, and  the  bell-jar  is  filled  with  dense  white  fumes  of 
phosphorus  pentoxide.  The  oxide  falls  as  a  white  powder 
on  the  plate  and  possesses  all  the  properties  of  the  product 
obtained  by  burning  yellow  phosphorus  under  the  same  con- 
ditions. 

P,  4-  5  O2  =  2  PA. 

Crucible  ;  plate  ;  bell-jar  ;  red  P. 

25.  Combustion  with  potassium  chlorate.  —  (a)  A  mixture 
of  red  phosphorus  and  potassium  chlorate  explodes  with 
heat  or  concussion. 

A  piece  of  white  paper  20  mm.  square  is  folded  in  the 
form  used  by  druggists  to  dispense  powders.  A  pinch  of 
finely  powdered  potassium  chlorate  and  about  one-third  the 
volume  of  red  phosphorus  are  placed  in  the  paper,  which  is 
very  carefully  folded  in  the  original  creases,  care  being 
taken  to  exert  no  pressure.  The  paper  is  then  placed  on 
an  anvil  and  struck  with  a  hammer  in  a  gloved  hand.  The 
report  is  quite  sharp. 


HYDROGEN    PHOSPHIDE  249 

The  union  between  red  phosphorus  and  potassium  chlo- 
rate may  be  brought  about  by  placing  a  small  pinch  of  each 
in  an  unglazed  mortar.  By  rubbing  the  ingredients  with  a 
pestle  in  the  gloved  hand  the  mixture  may  be  exploded. 

Folded  paper  ;  mortar  and  pestle ;  hammer  and  anvil ;  gauntlets ; 
red  P  ;  powdered  KCIO3. 

(6)  The  igniting  surface  of  a  safety  match-box  contains 
red  phosphorus. 

A  stick  of  potassium  chlorate  is  prepared  by  carefully 
melting  the  dry,  powdered  salt  in  a  small  test-tube.  After 
the  contents  of  the  tube  have  become  liquid  it  is  allowed  to 
cool,  and  the  glass  is  broken  off,  leaving  a  stick  of  solid  po- 
tassium chlorate.  Such  a  stick  when  rubbed  on  the  igniting 
surface  of  a  safety  match-box  produces  a  flash  of  fire.  If 
the  operation  is  conducted  over  a  Bunsen  burner  through 
which  gas  is  issuing,  the  spark  produced  by  the  friction  will 
ignite  the  gas. 

Stick  of  KCIO3  ;  safety  match-box. 


HYDROGEN    PHOSPHIDE 

ORMATION  AND  PREPARATION 

26.   By  the  action  of   hydrogen   on   red  phosphorus.  — 

Hydrogen  combines  with  red  phosphorus  directly  to  form 
hydrogen  phosphide. 

Dry  hydrogen  is  conducted  over  red  phosphorus  in  a  20 
cm.  length  of  combustion  tubing  fitted  with  a  cork  at  each 
end,  one  carrying  a  glass  tube  conducting  the  hydrogen,  the 
other  a  delivery -tube.  Hydrogen  is  first  passed  through  the 
system  until  all  air  is  expelled  and  then  the  red  phosphorus 
gently  heated.  Soon  sufficient  hydrogen  phosphide  is  formed 
to  render  the  gas  collected  in  cylinders  capable  of  ignition 


250  CHEMICAL    LECTURE   EXPERIMENTS 

by  fuming  nitric  acid.  If  the  end  of  the  delivery-tube  is 
allowed  to  dip  in  concentrated  nitric  acid,  the  gas  becomes 
ignited  as  it  comes  in  contact  with  the  air. 

P4  4,  6  H2  =  4  PH3. 

20  cm.  length  of  combustion  tubing  ;  H  generator  ;  red  P  ;  fuming 
HNO3. 

27.  From  phosphorus  and  alcoholic  potash.  —  Phosphorus 
acts  on  potassium  hydroxide,  forming  potassium  hypophos- 
phite  and  hydrogen  phosphide.  Certain  by-products  are 
formed  in  the  reaction  which  impart  to  the  hydrogen  phos- 
phide evolved  the  property  of  spontaneous  combustibility  on 
exposure  to  the  air.  This  by-product  (P2H4)  is  absorbed  by 
alcohol,  and  accordingly,  if  a  quantity  of  strong  alcohol  is 
added  to  the  potassium  hydroxide  used  in  the  reaction,  the 
issuing  gas  will  not  inflame  on  exposure  to  the  air. 

A  few  pieces  of  phosphorus  are  placed  in  a  100  cc.  Erlen- 
meyer  flask  fitted  with  a  one-holed  rubber  stopper  with  a 
delivery-tube.  The  phosphorus  is  covered  with  30  cc.  of 
strong  alcohol  to  which  15  cc.  of  concentrated  potassium 
hydroxide  solution  have  been  added.  The  flask  is  gently 
warmed,  and  as  soon  as  all  air  has  been  driven  out  the  cork 
is  inserted.  The  gas  collected  at  the  pneumatic  trough  is 
pure  hydrogen  phosphide.  Several  small  jars  should  be 
collected  for  use  in  experiments  on  the  properties  of  the 
pure  gas. 

P4  +  3  KOH  +  3  H2O  =  3  KH2PO2  +  PH3. 

100  cc.  Erlenmeyer  flask ;  small  cylinders  ;  con.  KOH  solution  ; 
alcohol ;  P. 

28.  Impure  hydrogen  phosphide  from  phosphorus  and 
sodium  or  potassium  hydroxide.  —  Impure  hydrogen  phos- 
phide is  especially  interesting  owing  to  its  spontaneous  in- 
flammability.   When  prepared  as  described  in  the  preceding 


HYDROGEN    PHOSPHIDE 


251 


experiment,  but  without  the  addition  of  alcohol,  a  gas  is  ob- 
tained consisting  chiefly  of  hydrogen  phosphide,  carrying  with 
it  small  quantities  of  a  liquid  hydrogen  phosphide  (P2H4) 
which  is  spontaneously  inflammable  on  exposure  to  the  air. 
Consequently  it  is  essential,  in  preparing  the  impure  gas,  to 
replace  all  air  in  the  apparatus  with  hydrogen,  coal  gas,  or 
other  oxygen-free  vapor. 

Two  or  three  5  mm.  pieces  of  phosphorus  in  a  300  cc.  Jena 
glass  flask  are  covered  with  100  cc.  of  concentrated  sodium  or 
potassium  hydroxide  solution.  Hydrogen  or  coal  gas  is 
passed  through  a  tube  in  a  two-holed  rubber  stopper  in 
the  neck  of  the  flask,  driving 
the  air  out  of  the  apparatus 
through  the  delivery-tube  (Fig. 
105).  When  all  air  has  been 
expelled,  the  supply  of  hydro- 
gen is  cut  off  and  the  flask  is 
gradually  heated.  When  the 
temperature  of  the  contents  of 
the  flask  is  near  the  boiling 
point  of  sodium  hydroxide, 
the  reaction  begins,  and  a  gas 
is  soon  regularly  evolved  and 
passes  over  into  the  pneumatic  trough.  The  first  bubbles 
of  gas  rising  through  the  water  in  the  trough  consist  chiefly 
of  hydrogen  and  present  no  special  appearance.  As  the 
hydrogen  is  expelled  and  the  hydrogen  phosphide  begins  to 
come  over,  each  bubble,  on  coming  in  contact  with  the  air,  is 
seen  to  take  fire,  burning  with  the  formation  of  a  white 
smoke.  If  the  reaction  is  so  regulated  that  the  individual 
bubbles  rise  through  the  liquid,  white  rings  rotating  in  a 
vortex  result  from  the  combustion  of  the  gas.  The  air 
should  be  as  free  as  possible  from  drafts  to  obtain  the  best 
results. 


Fig.  105 


252  CHEMICAL  LECTURE   EXPERIMENTS 

To  insure  the  formation  of  large  bubbles  the  delivery-tube, 
or  at  least  the  end  of  the  delivery-tube,  should  be  of  tubing 
of  not  less  than  8  mm.  internal  diameter.  On  an  ordinary 
tube  the  end  may  be  enlarged  by  connecting  to  it,  by  means 
of  a  rubber  tube,  a  wide  tip  of  glass  tubing.  The  heat  must 
be  so  regulated  that  the  gas  evolution  is  not  rapid  enough  to 
prevent  the  isolation  of  each  ring. 

At  the  end  of  the  experiment  hydrogen  may  be  passed 
through  the  apparatus  to  expel  the  hydrogen  phosphide,  the 
current  of  gas  being  continued  until  the  issuing  bubbles 
are  no  longer  ignited.  The  cork  is  then  removed  and  water 
added,  care  being  taken  not  to  wash  out  any  of  the  unused 
phosphorus,  which  should  be  carefully  washed  and  trans- 
ferred to  the  bottle  containing  phosphorus. 

Instead  of  using  a  current  of  hydrogen  the  air  may  be 
expelled  from  the  apparatus  by  adding  2  cc.  of  ether  to  the 
liquid  in  the  flask  before  heating.  In  that  case  at  the  end 
of  the  reaction  the  flask  is  allowed  to  become  perfectly  cold, 
care  being  taken  to  have  the  end  of  the  delivery -tube  a  con- 
siderable distance  under  water.  As  the  flask  cools,  water  is 
sucked  back  through  the  delivery-tube,  nearly  filling  the 
flask. 

Apparatus  (Fig.  105)  ;  wide  delivery-tube ;  H  generator ;  con. 
NaOH;  P;  ether. 

29.  Impure  hydrogen  phosphide  from  calcium  phosphide 
and  water.  —  Water  acts  on  calcium  phosphide,  with  the 
liberation  of  hydrogen  phosphide,  which,  as  it  is  not  pure, 
takes  fire  on  exposure  to  the  air. 

A  few  lumps  of  calcium  phosphide  are  thrown  into  a  small 
cylinder  containing  a  few  cubic  centimeters  of  water.  The 
reaction  is  very  rapid  and  large  quantities  of  gas  are  liber- 
ated. As  the  gas  comes  in  contact  with  the  air  at  the  mouth 
of  the  cylinder,  it  ignites  and  continues  to  burn. 


HYDBOGEN  PHOSPHIDE 


253 


The  impure  hydrogen  phosphide  thus  formed  may  be 
collected  if  the  calcium  phosphide  is  allowed  to  fall  into 
water  in  a  small  three-necked  Wolff  bottle.  One  neck  of 
the  bottle  is  provided  with  a  wide,  straight  glass  tube 
which  dips  beneath  the  surface  of  the  water  in  the  bottle. 
The  second  neck  is  provided  with  a  cork 
and  a  glass  elbow  connected  with  an 
illuminating  gas-jet,  and  the  third  neck 
carries  a  delivery-tube  leading  to  a  pneu- 
matic trough  (Fig.  106).  The  Wolff  bot- 
tle should  be  about  half  full  of  water. 
Illuminating  gas  is  first  passed  through 
the  system  until  all  air  is  removed.  The 
current  of  illuminating  gas  is  then  cut 
off,    and    lumps    of    calcium   phosphide  yiq.  106 

small  enough  to  pass  through  the  wide 
tube  are  then  allowed  to  fall  into  the  bottle.     Soon  suffi- 
cient hydrogen  phosphide  will  have  collected  in  the  bottle 
to  escape  at  the  pneumatic  trough,  where,  as  each  bubble 
comes  in  contact  with  the  air,  it  becomes  ignited.^ 

CasPa  +  3  H2O  =  3  CaO  +  2  PH3. 

Apparatus  (Fig.  106)  ;  small  3-necked  Wolff  bottle ;  wide  delivery- 
tube  ;   Ca3P2. 

30.  Action  of  calcium  phosphide  on  water.  —  The  rapidity 
of  the  action  of  calcium  phosphide  on  water  renders  it  diffi- 
cult to  obtain  well-formed  rings  in  the  combustion  of  the 
hydrogen  phosphide  formed  from  the  reaction.  By  enclosing 
the  lump  of  calcium  phosphide  in  a  piece  of  sheet  lead,  ac- 
cording to  the  method  described  in  Ex.  1,  p.  39,  where 
sodium  is  covered  with  sheet  lead,  the  action  of  the  water  is 
confined  to  one  point  on  the  surface  of  the  phosphide,  and 


1  See  note  concerning  delivery-tube  in  the  preceding  experiment. 


254  CHEMICAL   LECTURE   EXPERIMENTS 

hence  the  gas  evolution  is  mncli  more  regular.  A  lump  of 
calcium  phosphide  wrapped  in  this  manner  is  thrown  into 
water  in  a  crystallizing-dish.  As  the  bubbles  of  gas  rise 
they  are  ignited  and,  in  the  absence  of  drafts,  well-formed 
rings  may  be  obtained. 

Crystallizing-dish  ;  sheet  lead  ;  CagPg. 

31.  Purification  of  hydrogen  phosphide.  —  (a)  By  alcohol. 
The  impurity  in  hydrogen  phosphide,  which  causes  its  spon- 
taneous combustibility,  may  be  removed,  as  has  been  before 
stated,  by  conducting  the  impure  gas  through  alcohol.  The 
gas  is  conducted  through  alcohol  in  a  gas  washing-bottle 
from  which  all  air  has  been  expelled  by  a  current  of  hydro- 
gen or  coal  gas.  The  hydrogen  phosphide  issuing  from  the 
wash-bottle  will  be  found  to  be  so  far  deprived  of  its 
impurity  as  to  be  no  longer  spontaneously  combustible. 

(h)  By  hydrochloric  acid.  Concentrated  hydrochloric  acid 
acts  on  the  impurity  in  hydrogen  phosphide,  decomposing  it 
and  forming  a  solid  compound  of  phosphorus  and  hydrogen, 
which  is  deposited  as  a  yellowish  precipitate  in  the  hydro- 
chloric acid.  In  the  apparatus  used  in  the  above  experi- 
ment concentrated  hydrochloric  acid  instead  of  alcohol  is 
placed  in  the  gas  washing-bottle.  After  driving  out  the  air 
impure  hydrogen  phosphide  is  conducted  through  the  hydro- 
chloric acid.  The  impurity  is  decomposed,  a  yellow  precip- 
itate appears,  and  the  issuing  gas  is  no  longer  spontaneously 
inflammable. 

(c)  By  means  of  cold.  Impure  hydrogen  phosphide  when 
conducted  through  a  freezing-mixture  is  likewise  purified 
to  such  an  extent  that  it  is  no  longer  spontaneously  inflam- 
mable. The  small  quantity  of  liquid  hydrogen  phosphide 
present  in  the  gas  is  condensed  by  the  freezing-mixture. 


HYDROGEN  PHOSPHIDE  255 

A  current  of  impure  hydrogen  phosphide  is  conducted 
through  a  U-tube  immersed  in  a  freezing-mixture  of  salt  and 
ice.  The  issuing  gas  is  not  spontaneously  inflammable. 
The  condensed  impurity  is  present  in  such  small  quantities 
as  to  be  seen  only  after  a  long  passage  of  the  gas.  The 
tube  may  be  removed  from  the  freezing-mixture  while  the 
gas  is  still  passing  through  it  and  allowed  to  become  warm 
in  the  room,  when  it  will  be  observed  that  the  issuing  gas  is 
again  spontaneously  inflammable. 

2  gas  washing-bottles ;  U-tube  ;  supply  of  impure  PH3  ;  ice  and 
salt  ;  alcohol. 

PROPERTIES   OP   THE   PURE   GAS 

32.  Combustion  in  the  air.  —  A  cylinder  of  pure  hydrogen 
phosphide  is  ignited  by  applying  a  flame.  The  gas  burns 
with  a  bright  flame,  forming  white  clouds. 

33.  Ignition  by  heat.  —  A  glass  rod  whose  end  has  been 
heated  in  a  Bunsen  flame  causes  the  ignition  of  a  jar  of  hy- 
drogen phosphide  when  thrust  into  it. 

34.  Ignition  by  fuming  nitric  acid.  —  A  jar  of  hydrogen 
phosphide  is  instantly  ignited  when  a  glass  rod  which  has 
been  dipped  in  fuming  nitric  acid  is  thrust  into  it. 

.  35.  Ignition  by  chlorine.  —  Chlorine  reacts  with  hydrogen 
phosphide,  causing  an  ignition  of  the  gas. 

A  500  cc.  cylinder  is  filled  with  chlorine  into  which  is 
lowered  the  recurved  jet  from  which  issues  pure  hydrogen 
phosphide.  As  the  gas  comes  in  contact  with  the  chlorine, 
it  is  ignited  and  burns  with  a  greenish  light. 

The  experiment  may  be  varied  by  collecting  over  water 
25  cc.  of  chlorine  in  a  100  cc.  cylinder  and  allowing  individ- 
ual bubbles  of  pure  hydrogen  phosphide  to  rise  inside  the 
cylinder  and  come  in  contact  with  the  gas.     As  each  bubble 


256  CHEMICAL   LECTUKE   EXPERIMENTS 

of  gas  is  not  instantly  ignited,  the  cylinder  must  be  firmly 
held  to  resist  the  explosion  of  the  accumulated  quantity  of 
gas  in  the  cylinder. 

Recurved  jet ;  500  cc.  cylinder  of  chlorine  ;  100  cc.  cylinder  of  CI ; 
supply  of  PHg. 

36.  Action  with  bromine  vapor.  —  When  bromine  vapor 
is  allowed  to  come  in  contact  with  hydrogen  phosphide,  a 
violent  reaction  takes  place,  which  causes  the  ignition  of  the 
gas.  The  hydrogen  phosphide  used  in  this  experiment  must 
be  pure,  and  not  spontaneously  combustible.  A  rod  is  dipped 
in  bromine  and  then  thrust  into  a  small  cylinder  of  pure 
hydrogen  phosphide.     The  gas  is  immediately  ignited. 

Jar  of  pure  PHj ;  Br. 

37.  Ignition  by  silver  nitrate  solution.  —  When  a  strong 
solution  of  silver  nitrate  is  poured  into  a  cylinder  of  pure 
hydrogen  phosphide,  the  gas  is  ignited. 

One  or  two  cubic  centimeters  of  strong  silver  nitrate  so- 
lution are  poured  into  a  50  cc.  cylinder  of  pure  hydrogen 
phosphide.  The  gas  catches  fire  with  an  explosion,  and  a 
black  deposit  of  silver  phosphide  covers  the  walls  of  the 
cylinder. 

500  cc.  jar  of  pure  PH3  ;  AgNOs  solution  (concentrated). 

PROPERTIES    OF   THE  IMPURE   GAS 

38.  Explosion  in  air.  —  If  impure  hydrogen  phosphide  is 
allowed  to  come  in  contact  with  a  confined  volume  of  air, 
the  combustion  is  of  an  explosive  nature. 

A  100  cc.  glass  cylinder  is  filled  with  water  and  inverted 
in  a  pneumatic  trough.  A  few  bubbles  of  air  are  introduced 
into  the  cylinder,  and  then  individual  bubbles  of  impure 
hydrogen  phosphide  are  allowed  to  rise  and  come  in  contact 
with  the  air.     As  each  bubble  comes  to  the  surface,  a  slight 


HYDROGEN   PHOSPHIDE  257 

explosion  results,  and  accordingly  care  should  be  taken  that 
the  bubbles  of  the  hydrogen  phosphide  ascend  in  the  cylin- 
der only  one  at  a  time,  and  that  the  cylinder  is  firmly  held 
in  the  hand. 

100  cc.  cylinder ;  supply  of  impure  PHg. 

39.  Combustion  in  oxygen.  —  (a)  The  combustion  of  hy- 
drogen phosphide  in  pure  oxygen  may  be  effected  by  con- 
ducting the  gas  in  a  slow  stream  into  an  apparatus  consisting 
of  a  wide  glass  tube  carrying  a  two-holed  cork  in  one  end. 
Oxygen  is  conducted  through  one  hole,  and  the  second  hole 
carries  a  doubly  bent  glass  tube  having  a  few  drops  of 
mercury  sealing  the  bend.  The  apparatus  is  clamped  in 
an  upright  position,  and  a  gentle  stream  of  oxygen  is  con- 
ducted into  the  tube.  As  each  bubble  of  impure  hydrogen 
phosphide  passes  the  mercury  and  ascends  into  the  atmos- 
phere of  oxygen,  it  burns  with  a  brilliant  flash. 

Apparatus  (Fig.  87,  p.  199)  with  bent  tube ;  0  supply  ;  supply  of 
impure  PHg ;   Hg. 

(6)  If  impure  hydrogen  phosphide  is  allowed  to  come  in 
contact  with  a  confined  volume  of  oxygen,  the  union  is  of 
an  explosive  nature. 

A  stout-walled  100  cc.  cylinder  is  one-third  filled  with 
oxygen  at  a  metallic  pneumatic  trough.  Impure  hydrogen 
phosphide  is  conducted,  one  bubble  at  a  time,  under  the 
mouth  of  the  cylinder,  and  allowed  to  rise  and  come  in 
contact  with  the  oxygen.  The  combustion  is  very  sharp, 
making  it  necessary  to  hold  the  cylinder  down  hard  on  the 
bottom  of  the  pan.  The  slow  stream  of  hydrogen  phosphide 
required  for  this  experiment  is  best  secured  from  the  appa- 
ratus described  in  Ex.  29.  The  greatest  caution  must  be 
observed  to  prevent  an  excess  of  the  gas  from  rising  in  the 
cylinder. 

100  cc.  cylinder ;  O  supply  ;  supply  of  impure  PH3. 


258 


CHEMICAL  LECTURE  EXPERIMENTS 


(c)  A  100  cc.  cylinder  is  filled  with  oxygen,  covered  with 
a  pasteboard  cover,  and  then  one-fourth  filled  with  warm 
water.  A  few  centigrams  of  powdered  calcium  phosphide 
are  then  shaken  into  the  cylinder,  and  the  mouth  nearly 
closed  with  the  cardboard  cover.  The  liberated  hydrogen 
phosphide  coming  in  contact  with  the  oxygen  produces  a 
series  of  brilliant  flashes. 

100  cc.  cylinder  of  0  ;  CasPj. 


PHOSPHONIUM   IODIDE 

40.  Preparation.  —  The  action  of  hydrogen  phosphide  on 
iodine  produces  a  small  quantity  of  phosphonium  iodide, 
which  serves  to  illustrate  the  preparation  of  this  compound. 
A  current  of  pure  hydrogen  phosphide  is  conducted 
through  a  60  cm.  length  of  glass  tubing  2  cm.  in  diameter, 
containing  a  few  grams  of  iodine  near  the  entrance  end. 
The  iodine  is  gently  warmed  by  playing  a  low  Bunsen  flame 

on  the  tube  at  intervals 
of  10  to  15  seconds.  A 
25  cm.  length  of  the  tube 
near  the  open  end  is  cooled 
by  allowing  ice-water  to 
drop  on  a  piece  of  filter- 
paper  wrapped  around  it 
(Fig.  107).  If  the  cur- 
rent of  hydrogen  phos- 
phide is  rapid,  a  deposit 
of  transparent  crystals  of  phosphonium  iodide  will  appear 
in  the  cooled  portion  of  the  tube.  The  reaction  is  explained 
as  taking  place  in  two  steps :  the  first  in  which  hydrogen 
phosphide  and  iodine  unite  to  form  hydriodic  acid  and 
iodide  of  phosphorus ;  in  the  second  the  excess  of  hydro- 


-^cCE 


Fia.  107 


PHOSPHORUS   TRICHLORIDE  259 

gen  phosphide  combines  with  the  hydriodic  acid  to  form 
phosphonium  iodide. 

Apparatus  (Fig.  107)  ;  60  cm.  length  of  combustion  tubing;  supply 
of  pure  PH3  ;  I ;  ice. 

41.  Decomposition  by  water.  —  Water  decomposes  phos- 
phonium iodide  with  the  formation  of  hydrogen  phosphide 
and  hydriodic  acid. 

Two  or  three  grams  of  phosphonium  iodide  are  placed  in 
a  small  evaporating-dish  on  the  bottom  of  a  large  beaker  or 
battery  jar,  covered  with  a  cardboard  having  a  small  hole 
in  the  centre.  One  or  two  cubic  centimeters  of  water  are 
poured  from  a  test-tube  on  the  end  of  a  long  stick,  through 
the  hole  in  the  cardboard,  npon  the  phosphonium  iodide. 
At  first  a  hissing  is  heard,  which  is  followed  almost  imme- 
diately by  an  explosion. 

Large  beaker  or  battery  jar ;  cardboard  cover ;  evaporating-dish ; 
test-tube  on  stick  ;  PH4I. 

42.  Ignition  by  fuming  nitric  acid.  —  Fuming  nitric  acid 
oxidizes  phosphonium  iodide  with  the  liberation  of  iodine. 

One  gram  of  phosphonium  iodide  is  placed  on  a  watch- 
glass,  and  a  drop  of  fuming  nitric  acid  allowed  to  fall  on  it. 
The  oxidation  is  accompanied  by  a  slight  noise,  and  iodine 
fumes  are  liberated. 

Watch-glass  ;  PH4I ;  fuming  HNO3. 

PHOSPHORUS   TRICHLORIDE 

43.  Preparation.  —  By  the  action  of  dry  chlorine  on  phos- 
phorus, phosphorus  trichloride  is  formed.  The  experiment 
is  similar  to  that  in  which  sulphur  monochloride  is  formed 
(Ex.  33,  p.  148). 

Ten  grams  of  yellow  phosphorus  are  placed  in  a  300  cc. 
tubulated  retort  (Fig.   66j  p.  148),  the  neck  of  which  is 


260  CHEMICAL  LECTURE   EXPERIMENTS 

thrust  through  a  rubber  stopper  deep  into  a  filter-flask 
immersed  in  ice-water.  A  glass  elbow  extends  through  a 
cork  in  the  tubulature,  and  is  so  arranged  that  it  can  be 
readily  raised  or  lowered.  Carbon  dioxide  is  first  passed 
through  the  apparatus  and  then  a  current  of  dry  chlorine 
introduced.  The  phosphorus  should  be  melted  and  suffi- 
ciently heated  to  have  an  excess  of  phosphorus  vapor  rather 
than  of  chlorine,  as  otherwise  the  excess  of  chlorine  would 
tend  to  form  solid  phosphorus  pentachloride  instead  of  the 
liquid  trichloride.  The  tube  conducting  the  chlorine  into 
the  retort  is  depressed  until  it  nearly  touches  the  surface  of 
the  melted  phosphorus.  The  neck  of  the  retort  should  be 
tightly  inserted  in  the  neck  of  the  filter-flask  and  a  rubber 
tube  should  conduct  the  issuing  gas  from  the  side  tube  to  a 
flue  or  some  suitable  absorption  apparatus  filled  with  concen- 
trated sodium  hydroxide  solution.  As  the  chlorine  comes  in 
contact  with  the  phosphorus  vapor,  it  ignites  and  burns  with 
a  feeble  greenish  flame.  By  raising  the  chlorine  tube  an 
excess  of  chlorine  may  be  introduced  in  the  upper  part  of 
the  apparatus,  when  it  will  be  seen  that  the  neck  of  the  retort 
becomes  coated  with  crystals  of  phosphorus  pentachloride. 
In  order  to  avoid  the  excess  of  chlorine  it  is  best  to  stop  the 
operation  before  all  the  phosphorus  is  combined,  finally  cool- 
ing the  apparatus  in  a  current  of  carbon  dioxide. 

P,  4-  6  CI2  =  4  PCI3. 

Apparatus  (Fig.  66,  p.  148)  ;  300  cc.  retort  (tubulated);  filter-flask  ; 
CO2  generator  ;  CI  supply  ;  ice-water  ;  yellow  P. 

44.  Decomposition  by  water.  —  Phosphorus  trichloride  is  a 
colorless  liquid  somewhat  heavier  than  water  and  not  imme- 
diately miscible  with  it. 

Three  cubic  centimeters  of  the  chloride  are  placed  in  a 
test-tube  and  covered  with  18  cc.  of  water.     The  phosphorus 


PHOSPHORUS   PENTACHLORIDE 


261 


trichloride  remains  in  the  bottom  of  the  tube  and  does  not 
mix  with  the  water.  On  warming  the  tube  with  the  hand, 
the  water  and  the  trichloride  soon  react,  liberating  bubbles  of 
hydrochloric  acid  gas,  which  are  absorbed  before  they  reach 
the  top  of  the  liquid.  By  immersing  the  test-tube  in  ice- 
water  the  reaction  can  be  entirely  stopped.  Decomposition 
again  ensues  on  warming.  If  the  decomposition  is  allowed 
to  continue,  the  liquid  soon  becomes  warm,  and  ultimately 
the  phosphorus  trichloride  is  completely  converted  to  phos- 
phorous and  hydrochloric  acids.  The  presence  of  phosphorous 
acid  may  be  established  by  adding  a  few  drops  of  gold  chlo- 
ride solution,  which  will  be  reduced  on  warming. 

PCI3  -f  3  H2O  =  H3PO3  +  3  HCl. 

PCI3;  ice-water ;  AuCls  solution. 


PHOSPHORUS  PENTACHLORIDE 


PREPARATION 

45.  By  the  combustion  of  phosphorus  in 
chlorine.  —  A  small  piece  of  phosphorus  is 
lowered  into  a  liter  flask  filled  with  dry 
chlorine  and  provided  with  a  cork  carrying 
a  calcium  chloride  tube.  The  phosphorus 
takes  fire  and  burns  in  the  excess  of  chlorine 
to  form  phosphorus  pentachloride,  which  will 
remain  as  a  white  powder  on  the  walls  of  the 
flask  (Fig.  108).  In  order  to  insure  an  excess 
of  chlorine  a  piece  of  phosphorus  having  a  di- 
ameter of  not  more  than  2  mm.  must  be  used. 

P,-f  10Cl2  =  4PCl5. 

Deflagrating-spoon  ;  liter  flask  of  dry  CI ;  cork 
with  CaCl2  tube ;  2  mm.  piece  of  yellow  P. 


Fia.  108 


262 


CHEMICAL  LECTURE  EXPERIMENTS 


46.   By  the  action  of  chlorine  on  phosphorus  trichloride.  — 

As  was  seen  in  Ex.  43  an  excess  of  chlorine,  when  that  ele- 
ment is  acting  on  phosphorus,  produces  the  pentachloride 
rather  than  the  trichloride  of  phosphorus.  Accordingly  it 
is  only  necessary  in  preparing  the  pentachloride  to  act  on 
the  trichloride  with  an  excess  of  chlorine. 

The  union  of  chlorine  and  phosphorus  trichloride  to  form 
the  solid  phosphorus  pentachloride  may  be  effected  by  pour- 
ing 3  cc.  of  phosphorus  trichloride  into  a  liter  flask  filled 
with  dry  chlorine.  A  cork  carrying  a  tube  filled  with  cal- 
cium chloride  (Fig.  108)  is  immediately  inserted  in  the 
neck  of  the  flask,  which  is  then  allowed  to  stand.  After  a 
few  minutes  the  color  will  nearly  all  disappear  from  the 
flask,  and  the  phosphorus  pentachloride  will  remain  as  a 
solid  mass  on  the  bottom  and  walls. 

PCI3  +  CI2  =  PCI5. 

Cork  and  CaCla  tube  ;  liter  flask  of  dry  CI ;  3  cc.  PCI3. 


Fig.  109 


PROPERTIES 

47.  Sublimation.  —  Phosphorus  penta- 
chloride sublimes  without  melting.  A 
small  quantity  of  the  powder  is  heated 
in  a  test-tube,  which  is  loosely  corked. 
A  sublimate  soon  appears  on  the  upper 
part  of  the  tube. 

48.  Decomposition  of  phosphorus  penta- 
chloride by  water.  —  If  a  small  quantity 
of  water  is  allowed  to  drop  on  phosphorus 
pentachloride,  the  decomposition  is  very 
violent,  resulting  in  the  formation  of  the 
oxychloride. 

The  apparatus  shown  in  Fig.  109  con- 


PHOSPHORUS  BROMIDES  2^'6 

sists  of  a  wide-mouthed  bottle  with  a  cardboard  cover  in 
which  an  opening  is  made  large  enough  to  admit  a  test- 
tube.  A  few  grams  of  the  pentachloride  are  placed  in  the 
test-tube  and  1  drop  of  water  from  a  long  bent  glass  tube 
is  allowed  to  fall  upon  it.  To  prevent  particles  of  the 
material  from  flying  about,  a  large  funnel  having  a  cork  in 
its  stem  is  suspended  mouth  downwards  over  the  test-tube. 
As  more  water  is  added,  the  conversion  to  phosphoric  and 
hydrochloric  acids  becomes  complete,  the  liquid  remaining 
in  the  test-tube  consisting  of  mixture  of  these  two  acids. 

Phosphorus  pentachloride,  when  allowed  to  drop  into  a 
large  mass  of  water,  hisses  and  undergoes  decomposition,  re- 
sulting in  the  formation  of  phosphoric  and  hydrochloric  acids. 

Apparatus  (Fig.  109)  ;  PCI5. 

PHOSPHORUS   BROMIDES 

49.  Preparation  of  phosphorus  tribromide  by  the  union  of 
phosphorus  and  bromine.  —  (a)  Phosphorus  and  bromine 
unite  with  explosive  violence,  and  while  no  quantity  of  phos- 
phorus tribromide  can  be  prepared  by  this  method,  the  inter- 
action of  the  two  elements  may  be  shown  by  placing  1  cc. 
of  bromine  in  the  test-tube  of  the  apparatus  (Fig.  109) 
and  introducing  a  2  mm.  piece  of  yellow  phosphorus 
by  means  of  a  long  stick.  The  phosphorus  is  immediately 
ignited,  and  as  a  rule  blown  out  of  the  tube  into  the  funnel. 
Care  must  be  taken  to  avoid  danger  from  the  burning  phos- 
phorus, and  the  hands  should  be  protected  with  gloves. 

P4  -f-  6  Brs  =  4  PBrg. 

Apparatus  (Fig.  109)  ;  long  stick  ;  Br;  yellow  P. 

(6)  The  explosive  violence  of  the  reaction  between  phos- 
phorus and  bromine  may  be  considerably  modified  by  add- 
ing the  bromine  to  phosphorus  under  water. 


264  CHEMICAL   LECTURE   EXPERIMENTS 

A  3  mm.  piece  of  yellow  phosphorus  is  placed  in  the  test- 
tube  of  the  apparatus  used  in  the  preceding  experiment  and 
covered  with  10  cc.  of  water.  Five  drops  of  bromine  are 
poured  from  a  test-tube  on  the  end  of  a  stick  upon  the  phos- 
phorus. The  reaction  is  very  vigorous,  and  a  flame  is  seen 
under  the  water  as  the  two  elements  unite.  In  case  the 
bromine  is  not  in  excess,  the  presence  of  phosphorous  acid  in 
the  solution  may  be  shown  by  testing  with  gold  chloride 
solution. 

(c)  Phosphorus,  when  lowered  into  bromine  vapor,  ignites 
of  itself  and  forms  phosphorus  tribromide,  which,  in  excess 
of  bromine,  becomes  converted  to  phosphorus  pentabromide. 

A  liter  flask  is  filled  with  bromine  vapor  by  introducing  a 
few  drops  of  bromine  and  then  warming  the  flask  to  expel 
the  air.  A  3  mm.  piece  of  well-dried  phosphorus  is  placed 
in  a  deflagrating-spoon  attached  to  a  cork  and  then  lowered 
into  the  bromine  vapor.  After  a  few  moments  the  phospho- 
rus catches  fire  of  itself  and  burns  with  a  yellowish  flame. 

Liter  flask ;  deflagrating-spoon  j  Br  ;  P. 

PHOSPHOROUS   ACID 

PREPARATION 

50.  By  the  slow  oxidation  of  phosphorus.  —  The  energetic 
oxidation  of  phosphorus  produces  phosphorus  pentoxide, 
which,  in  the  presence  of  water,  forms  phosphoric  acid.  If 
phosphorus  is  allowed  to  oxidize  slowly  in  the  air,  as  in  Ex. 
32,  p.  33,  in  the  preparation  of  ozone,  the  higher  state  of 
oxidation  is  not  reached  and  considerable  quantities  of  phos- 
phorous acid  are  formed.  The  water  remaining  in  the  flask 
after  the  preparation  of  ozone,  when  tested  with  gold 
chloride  solution,  shows  the  presence  of  phosphorous  acid. 
The  ozone  apparatus   should  be  arranged  and   allowed  to 


PHOSPHOROUS   ACID  265 

stand,  if  possible,  over  night,  when  a  strong  test  for  phos- 
phorous acid  may  be  obtained. 

p,+302  =  2PA.  m 

3  H2O  +  PA  =  2  H3PO3.     [?] 
Ozone  apparatus  (Fig.  14,  p.  34)  ;  AuCls ;  P. 

51.   By  the  action  of  phosphorus  trichloride  on  water. — 

Water  reacts  energetically  with  phosphorus  trichloride,  form- 
ing phosphorous  acid  and  hydrochloric  acid.  The  hydro- 
chloric acid  liberated  is  to  a  large  extent  absorbed  by  the 
water  used  in  the  operation,  though,  by  boiling,  the  excess 
of  gas  may  be  driven  off,  leaving  a  solution  containing  phos- 
phorous and  hydrochloric  acids. 

A  few  cubic  centimeters  of  phosphorus  trichloride  are  al- 
lowed to  fall  from  a  dropping-funnel  into  20  cc.  of  water  in 
a  small  distilling-flask.  The  dropping-funnel  is  inserted  in 
the  neck  of  the  flask  in  a  one-holed  rubber  stopper,  and  the 
side  tube  of  the  flask  should  be  provided  with  a  rubber  tube 
to  conduct  away  the  hydrochloric  acid  fumes  that  are  formed. 
As  the  phosphorus  trichloride  comes  in  conta<;t  with  the 
water,  a  vigorous  reaction  takes  place  and  large  quantities  of 
hydrochloric  acid  are  liberated.  On  removing  the  dropping- 
funnel  and  corking  the  neck  of  the  flask,  the  contents  may 
be  brought  to  a  boil  and  the  excess  of  hydrochloric  acid 
driven  oif.  The  liquid  will  now  give  strong  tests  for  phos- 
phorous acid.  A  small  portion  of  the  liquid  heated  in  a 
test-tube  gives  off  first  hydrochloric  acid  and  then  water. 
Finally,  if  the  heating  is  carried  to  a  sufficient  degree,  the 
phosphorous  acid  will  decompose,  yielding  hydrogen  phos- 
phide, which  may  be  ignited  at  the  mouth  of  the  test-tube. 

PCI3  4-  3  H2O  =  H3PO3  +  3  HCl. 

Dropping-funnel ;  200  cc.  distilling-flask ;  PCL. 


266  CHEMICAL    LECTURE    EXPERIMENTS 


HYPOPHOSPHOROUS   ACID 

52.  Preparation  of  the  sodium  or  potassium  salts  by  the 
reaction  between  phosphorus  and  the  alkaline  hydroxides.  — 
See  Exs.  27  and  28. 

53.  Reduction  of  sulphurous  acid  by  sodium  hypophosphite. 

—  Hypophosphorous  acid  and  its  salts  are  very  strong  re- 
ducing agents.  Sulphurous  acid,  itself  a  strong  reducing 
agent,  is  reduced  by  solutions  of  sodium  hypophosphite. 

Strong  sulphur  dioxide  water  is  treated  with  a  solution  of 
sodium  hypophosphite  and  gently  warmed  in  a  test-tube. 
The  reaction  requires  a  little  time  for  its  completion,  but 
soon  a  precipitate  of  sulphur  is  obtained. 

Solution  of  NaH2P02  j  SO2  water. 


PHOSPHORUS   PENTOXIDE    AND    PHOSPHO- 
RIC   ACIDS 

54.  Preparation  of  phosphorus  pentoxide  by  combustion  of 
phosphorus  in  air.  —  See  Ex.  26,  p.  29. 

55.  Sublimation  of  phosphorus  pentoxide. — Phosphorus 
pentoxide,  on  heating,  sublimes  without  melting. 

A  small  quantity  of  the  powder  is  placed  in  a  clean,  dry 
test-tube  and  heated.  The  oxide  sublimes  on  the  upper 
part  of  the  tube,  while  the  residue,  which  is  combined  with 
a  small  quantity  of  water,  melts  in  the  form  of  glacial  phos- 
phoric acid. 

56.  Evolution  of  heat  by  the  action  of  phosphorus  pen- 
toxide on  water.  —  When  water  is  added  to  phosphorus 
pentoxide,  sufficient  heat  is  generated  to  ignite  a  piece  of 
guncotton. 


PHOSPHORUS    PENTOXIDE  267 

A  small  heap  of  the  pentoxide  is  placed  on  a  watch-glass 
and  a  piece  of  guncotton  laid  on  it  (Fig.  110).  Water  is 
allowed  to  drop  on  the  oxide  from 
the  tip  of  a  glass  tube  drawn  out  to 
a  fine  jet.  As  the  first  drop  of  water 
comes  in  contact  with  the  powder, 
the  heat  generated  ignites  the  gun- 
cotton. 


Watch-glass  ;  P2O5  ;  guncotton. 

57.  Preparation  of  phosphoric  acids  by  the  action  of  water 
on  phosphorus  pentoxide.  —  Phosphorus  pentoxide  when 
added  to  water  combines  with  it,  forming  phosphoric  acid. 

Phosphorus  pentoxide  is  allowed  to  fall  in  small  quanti- 
ties into  50  cc.  of  cold  water  in  a  beaker.  As  each  particle 
comes  in  contact  with  the  water,  it  hisses.  Not  all  the  oxide 
is  dissolved,  as  white  flocks  appear  in  the  liquid.  The  liquid 
is  divided  into  two  equal  parts,  one  of  which  is  brought  to 
the  boiling  point;  the  other  is  filtered.  On  heating,  the 
white  flocks  all  disappear,  and  the  solution  then  contains  or- 
dinary orthophosphoric  acid. 

The  filtrate  from  the  filtered  portion  contains  metaphos- 
phoric  acid,  which  gradually  becomes  converted  to  the  ortho 
acid.  This  conversion  is,  as  might  be  expected,  instanta- 
neous upon  heating. 

3H20  +  PA  =  2H3P04. 
H20-f-PA  =  2HP03. 


AESENIC 


ARSENIC 

1.  Purification  of  commercial  arsenic.  —  (a)  Commercial 
arsenic  is  generally  a  dull  black,  and  in  order  to  exhibit  the 
metallic  lustre  of  this  element  the  coating  must  be  removed. 
This  is  readily  accomplished  by  heating  the  arsenic  with  a 
strong  solution  of  potassium  dichromate  to  which  some  sul- 
phuric acid  has  been  added.  The  purified  material  should 
be  washed  thoroughly  with  water  and  then  dried  with  alco- 
hol and  ether. 

Commercial  As  ;  K2Cr207  solution  ;  alcohol ;  ether. 

(6)  A  solution  of  sodium  hypochlorite  may  be  used  in 
place  of  the  acidulated  potassium  dichromate. 

(c)  The  dull  coating  on  commercial  arsenic  may  also  be 
removed  by  heating  the  arsenic  with  a  small  quantity  of 
iodine  in  a  hard-glass  test-tube.  The  iodine  first  sublimes 
and  covers  the  arsenic  with  a  yellowish  coating  of  arsenic 
iodide,  which,  on  further  heating,  sublimes  in  the  upper  por- 
tion of  the  tube  as  a  reddish  sublimate  of  arsenic  tri-iodide. 
The  arsenic  is  by  this  operation  purified,  and  remains  as  a 
bright  metallic-looking  mass  in  the  test-tube. 

But  a  small  quantity  of  iodine  is  needed  for  this  operation, 
and  in  a  few  minutes  a  large  quantity  of  the  impure  com- 
mercial arsenic  may  be  rendered  clean  and  bright. 

Hard-glass  test-tube  ;  As  ;  I. 

268 


ARSENIC   HYDRIDE  269 

2.  Sublimation.  —  Arsenic,  though  commonly  obtained  as 
a  dull  black  mass,  sublimes  on  heating  to  form  a  crystal- 
line metallic  deposit. 

A  few  pieces  of  arsenic  are  heated  in  a  dry  hard-glass  test- 
tube  with  the  burner  and  the  chimney  shown  in  Fig.  2,  p.  8. 
A  portion  of  the  arsenic  sublimes  and  condenses  on  the 
upper  part  of  the  tube,  that  part  of  the  sublimate  nearest 
the  source  of  heat  having  a  brilliant  metallic  lustre  and  crys- 
talline structure,  while  farther  up  the  tube  the  deposit  is  of 
a  dull  gray  amorphous  nature. 

Burner  and  chimney  (Fig.  2,  p.  8) ;  hard-glass  test-tube  ;  As. 


ARSENIC   HYDRIDE    (ARSINE) 

3.  Preparation.  —  Nascent  hydrogen  reduces  solutions 
containing  arsenic  to  arsenic  hydride,  which  is  given  off  as 
a  gas  with  the  excess  of  hydrogen.  The  extremely  poi- 
sonous nature  of  this  gas  renders  it  necessary  to  prepare 
it  on  a  very  small  scale  only,  and  to  destroy  it  before  it  is 
allowed  to  escape  into  the  room. 

A  hydrogen  generator  may  be  set  in  operation  and  the 
gas,  after  being  conducted  through  a  chloride  of  calcium 
tube,  may  be  ignited  at  a  glass  jet,  taking  all  precautions  to 
prevent  an  explosion.  Since  the  flame  coloration  is  an 
essential  feature  of  this  experiment,  the  tube  should  be 
provided  with  a  platinum  tip  or  be  replaced  by  a  metallic 
blowpipe  jet,  as  otherwise  the  naturally  colorless  hydrogen 
flame  would  melt  the  glass  and  become  colored  yellow  with 
sodium.  On  adding  a  few  drops  of  a  solution  containing 
arsenic  the  flame  will  be  colored  a  bright  blue  by  the  pres- 
ence of  arsine  in  the  issuing  gas. 

A  much  more  satisfactory  method  of  experimenting  with 
this  gas  is  shown  in  Fig.  111.    A  small  wide-mouthed  bottle, 


270 


CHEMICAL   LECTURE   EXPERIMENTS 


containing  a  few  grams  of   granulated  zinc  covered   with 
water,  is  provided  with  a  three-holed  cork.     Hydrogen  is 

conducted  from  a  Kipp  gener- 
ator through  a  glass  elbow  in 
one  of  the  holes  in  the  cork 
and  issues  through  a  second 
elbow  provided  with  a  calcium 
chloride  tube  and  a  jet  with 
a  platinum  tip.  A  small  this- 
tle-tube is  inserted  in  the  third 
hole  of  the  cork,  its  lower  end 
being  sealed  with  water.  Hy- 
drogen is  conducted  through  the  apparatus  until  all  air 
is  removed,  and  then  sufficient  hydrochloric  acid  is  poured 
through  the  thistle-tube  to  produce  a  slow  evolution  of  hydro- 
gen in  the  bottle.  On  adding  a  few  drops  of  a  solution  con- 
taining arsenic,  arsine  will  be  formed  and  will  be  conducted, 
along  with  the  main  hydrogen  current,  to  the  platinum  jet, 
where  it  will  impart  a  blue  color  to  the  flame. 


Fig.  Ill 


H  generator; 
AsCla  solution. 


Kipp  generator  for  H;    apparatus  (Fig.  Ill);  Zn  ; 


4.  Decomposition  by  heat.  —  When  arsine,  or  its  mixture 
with  hydrogen,  is  conducted  through  a  glass  tube  which  is 
strongly  heated,  the  arsine  is  decomposed,  liberating  hydro- 
gen, and  arsenic  is  deposited  on  the  colder  portions  of  the 
tube. 

A  jet  is  prepared  by  drawing  a  piece  of  7  mm.  hard-glass 
tubing  out  to  a  fine  point.  The  end  of  the  fine  jet  is  bent 
at  right  angles,  and  the  jet  is  then  connected  to  the  calcium 
chloride  tube  in  the  apparatus  (Fig.  111).  On  passing 
hydrogen  mixed  with  arsine  through  the  tube  and  heating  it 
strongly  with  a  Bunsen  burner,  the  arsenic  will  be  deposited 
as  a  metallic  mirror  in  the  constricted  portion  of  the  tube. 


ARSENIC    SULPHIDE  271 

If  the  current  of  arsine  is  not  too  rapid,  all  of  the  arsenic 
may  be  deposited  in  this  manner,  and  consequently  the  color 
of  the  flame  changed.  For  this  purpose,  however,  it  is  bet- 
ter to  use  a  jet  of  the  form  shown  in  Fig.  Ill,  which  is  pref- 
erably made  out  of  hard-glass  tubing.  The  hydrogen  should 
be  ignited  at  the  platinum  jet  and  the  characteristic  color 
of  the  arsine  flame  noted.  On  strongly  heating  the  tube 
half  way  between  the  bend  and  the  calcium  chloride  tube, 
the  arsine  will  be  decomposed,  the  arsenic  deposited  between 
the  flame  and  the  bend,  and  the  color  of  the  arsine  flame 
will  disappear,  leaving  the  colorless  flame  of  hydrogen. 

4  AsHg  =  As4  +  6  Hj. 

AsHs  apparatus  (Fig.  Ill)  ;  hard-glass  tubing  (7  mm.);  Pt  jet. 

5.  Deposition  of  arsenic  by  cooling  a  flame  containing 
arsine.  —  If  a  cold  porcelain  dish  is  held  in  the  flame  of 
arsine  burning  at  the  jet  in  Fig.  Ill,  arsenic  will  be  depos- 
ited as  a  dark,  metallic-appearing  spot,  which  may  be 
removed  by  the  addition  of  a  few  drops  of  sodium  hypo- 
chlorite solution,  or  by  gently  warming  with  nitric  acid  of  a 
specific  gravity  1.25.  (For  further  consideration  of  arsenic 
spots,  see  under  antimony,  Ex.  3.) 


ARSENIC   SULPHIDE 

6.  Commercial  arsenic  sulphide  in  white  fire.  —  Two  parts 
of  commercial  arsenic  sulphide  (realgar,  AsgSa),  when 
mixed  with  two  parts  of  sulphur  flowers  and  four  parts  of 
potassium  nitrate,  form  a  mixture  which,  on  ignition,  gives 
an  intense  white  light. 

Powdered  realgar ;  KNO3  ;  S  flowers. 


272 


CHEMICAL  LECTURE  EXPERIMENTS 


ARSENIC   TRIOXIDE 


7.   From  the  combustion  of  arsenic  in  oxygen.  —  Arsenic, 
when  strongly  heated  in  an  atmosphere  of  oxygen,  burns, 
forming  arsenic  trioxide. 

The  combustion  of  arsenic  in  oxygen 
and  the  sublimation  of  the  arsenic  tri- 
oxide are  shown  by  heating  a  small 
quantity  of  the  element  in  a  40  cm. 
glass  tube  15  mm.  internal  diameter, 
sealed  at  one  end.  The  tube  is  fitted 
with  a  two-holed  cork  carrying  a  long 
elbow  extending  nearly  to  the  bottom 
of  the  tube  and  a  short  glass  elbow  con- 
nected with  a  flue  (Fig.  112).  The  tube 
is  clamped  in  an  inclined  position  and 
a  current  of  oxygen  conducted  through 
^  it.     On  heating  the  arsenic,  it  catches 

^^  II  fire  and  burns  brilliantly.     Some  of  the 

arsenic  is  volatilized  and  deposited  as  a 
crystalline  sublimate  in  the  cooler  por- 
tions of  the  tube.  A  considerable  quantity  of  the  arsenic 
trioxide  formed  is  deposited  as  a  white  sublimate  in  the 

tube. 

As4  -f  3  O2  =  2  AS2O3. 


Fig.  112 


40  cm.  glass  tube  15  mm.  diameter ;  cork  and  tubes  j  0  supply  ;  As. 


ANTIMONY 


ANTIMONY 

1.  Fusibility.  —  Antimony  is  easily. melted  with  a  blow- 
pipe by  directing  the  flame  upon  a  small  piece  of  the  metal 
placed  in  a  cavity  scooped  out  of  a  piece  of  charcoal.  The 
strongly  heated  globule,  if  allowed  to  fall  upon  a  piece  of 
white  paper,  breaks  into  numerous  small  globules,  which 
run  in  all  directions,  each  globule  charring  the  paper  over 
which  it  runs.  A  large  pasteboard  box  cover  may  be  used, 
or  the  edges  of  the  paper  may  be  turned  up  to  prevent  the 
particles  of  antimony  from  running  all  over  the  table. 

White  paper  or  box  cover ;  blowpipe  ;  charcoal ;  Sb. 

2.  Combustion  of  powdered  antimony.  —  Pulverized  anti- 
mony, when  blown  through  a  Bunsen  flame,  burns  brilliantly, 
giving  a  white  light.  The  finely  powdered  metal  is  placed  in 
a  glass  elbow,  such  as  is  described  in  Ex.  18,  p.  24,  and  blown 
lengthwise  through  the  flame,  either  by  a  puff  of  air  from 
the  mouth  or  better  by  oxygen  from  a  cylinder. 

Glass  elbow  ;  powdered  Sb  ;  0  supply. 

ANTIMONY   HYDRIDE    (STIBINE) 

3.  Preparation.  —  The  preparation  of  pure  antimony 
hydride  is  never  attempted,  as  hydrogen  containing  a  small 
quantity  of  the  gas  gives  all  the  characteristic  tests  of  the 
hydride  itself.     When  hydrogen  is  generated  in  solutions 

T  273 


274  CHEMICAL   LECTURE   EXPERIMENTS 

containing  antimony,  a  portion  of  the  antimony  is  converted 
to  stibine,  which  escapes  with  the  hydrogen. 

The  apparatus  used  is  similar  to  that  described  for  arsine 
(Ex.  3,  p.  270).  Hydrogen  is  generated  in  an  Erlenmeyer 
flask,  fitted  with  a  cork  and  a  thistle-tube,  by  means  of  zinc 
and  sulphuric  acid.  The  issuing  gas  is  dried  with  calcium 
chloride  and  burned  at  a  jet.  A  few  drops  of  antimony 
chloride  solution  are  introduced  through  a  funnel,  and  in  a 
few  moments  the  color  of  the  flame  will  be  considerably 
changed  and  a  white  smoke,  consisting  chiefly  of  antimony 
trioxide,  will  ascend.  The  reactions  of  stibine  are  very  simi- 
lar to  those  of  arsine. 

A  cold  porcelain  dish  held  in  the  flame  produces  a  dull 
black  deposit  of  antimony,  distinguished  from  the  arsenic 
spots,  which  have  a  more  metallic  lustre,  by  being  insoluble 
in  a  solution  of  sodium  hypochlorite. 

If  the  gas  is  conducted  through  a  heated  gla^s  tube,  the 
antimony  will  be  deposited  as  a  black  mirror  on  the  tube ; 
but  while  arsenic  is  only  deposited  on  that  portion  of  the 
tube  nearer  the  exit,  antimony  will  be  deposited  on  both 
sides  of  the  heated  portions  of  the  tube. 

The  gas,  when  conducted  through  a  glass  elbow  dipping 
into  a  beaker  of  silver  nitrate  solution,  produces  a  black 
precipitate  of  silver  antimonide. 

The  distinction  between  the  reactions  of  the  arsenic  and 
antimony  spots  with  sodium  hypochlorite  is  markedly  shown 
by  holding  a  white  dinner  plate  in  the  stibine  flame  and 
moving  it  in  such  a  way  that  the  symbol  of  antimony  (Sb) 
will  be  written  in  the  form  of  a  black  deposit  on  the  plate. 
The  plate  should  then  be  held  in  an  arsine  flame  and  the 
antimony  entirely  covered  with  a  deposit  of  arsenic.  On  pour- 
ing sodium  hypochlorite  solution  into  the  plate,  the  arsenic 
deposit  is  completely  dissolved,  and  the  antimony  deposit 
unaffected  stands  out  as  originally  deposited. 


ANTIMONY   TRISULPHIDE  275 

If  arsine  as  well  as  stibine  is  present  in  the  burning  hy- 
drogen, both  elements  will  be  deposited  on  a  cold  dish  held 
in  the  flame.  If,  however,  the  dish  is  held  in  a  vertical 
position  and  the  spot  deposited  in  an  elongated  form,  the 
arsenic,  by  reason  of  its  greater  volatility,  will  be  chiefly  de- 
posited in  the  upper  portions  of  the  spot.  If  sodium  hypo- 
chlorite is  allowed  to  act  on  such  a  deposit,  the  outer  and 
upper  portions  will  be  seen  to  disappear,  while  the  lower 
portions,  consisting  as  they  do,  chiefly  of  antimony,  remain 

unacted  upon. 

2  SbHg  =  2  Sb  +  3  H2. 

4  AsHg  =  AS4  +  6  H2. 

Erlenmeyer  flask  ;  thistle-  and  delivery- tubes  ;  evaporating-dish  ; 
plate  ;  hard-glass  tube  ;  SbCls  sol. ;  NaClO  sol.  ;  AsHg  generator. 

ANTIMONY    CHLORIDES 

4.  Combustion  of  antimony  in  chlorine.  —  Finely  divided 
antimony  burns  brightly  in  chlorine,  forming  antimony 
trichloride  and  pentachloride. 

A  small  quantity  of  antimony  powder  is  sifted  from  a 
cheese-cloth  bag  into  a  500  cc.  cylinder  filled  with  chlorine 
and  placed  in  a  strong  draft.  As  each  particle  of  antimony 
falls  into  the  chlorine,  it  burns  with  a  bright  light,  forming 
antimony  trichloride,  which,  in  the  presence  of  an  excess  of 
chlorine,  is  converted  to  the  pentachloride. 

2  Sb  +  3  CI2  =  2  SbClg. 

2  Sb  +  5  CI2  =  2  SbClfi. 

Jar  of  CI ;  finely  powdered  Sb. 

ANTIMONY   TRISULPHIDE 

5.  Combustion  in  a  current  of  oxygen.  —  Antimony  trisul- 
phide,  owing  to  the  oxidizable  nature  of  both  of  its  elements, 


276  CHEMICAL  LECTURE  EXPERIMENTS 

burns  brilliantly  in  oxygen,  forming  antimony  trioxide  and 
sulphur  dioxide. 

Dry  antimony  trisulphide  is  heated  in  a  bulb-tube  in  a 
current  of  oxygen.  The  sulphide  soon  takes  fire  and  burns 
brilliantly.  The  issuing  gas  may  be  tested  for  the  presence 
of  sulphur  dioxide  by  a  paper  dipped  in  potassium  dichro- 
mate  solution.  The  antimony  trioxide  formed  is  given  off 
as  a  white  smoke,  which  escapes  from  the  tube,  though  a 
portion  of  the  oxide  is  deposited  as  a  white  sublimate. 

2  SbgSs  +  9  O2  =  2  SbaOg  +  6  SO2. 

Bulb-tube  ;  O  supply ;  K2Cr207  solution  ;  Sb2S3. 

6.  Combustion  in  fused  potassium  nitrate.  —  Antimony 
sulphide  is  readily  oxidized  by  being  dropped  into  fused 
potassium  nitrate.  A  small  quantity  of '  the  potassium 
nitrate  is  fused  in  a  hard-glass  test-tube  which  is  clamped 
in  a  vertical  position,  and  antimony  sulphide  in  the  form 
of  a  fine  powder  is  shaken  into  the  tube.  As  the  sulphide 
comes  in  contact  with  the  potassium  nitrate,  it  burns  with 
a  brilliant  light.  Potassium  chlorate  may  be  substituted 
for  potassium  nitrate. 

Hard-glass  test-tube,  clamped  ;  KNO3  ;  KCIO3  ;  Sb2S3. 

7.  Use  in  Bengal  fires.  —  Native  antimony  sulphide, 
when  powdered  and  mixed  with  sulphur  flowers  and  potas- 
sium nitrate,  gives  on  ignition  an  intense  white  light. 

One  gram  of  finely  powdered  stibnite  is  mixed  on  a  paper 
with  2  g.  of  fiowers  of  sulphur  and  7  g.  of  finely  pow- 
dered potassium  nitrate,  avoiding  all  unnecessary  press- 
ure or  friction.  The  mixed  powder  is  placed  on  an  asbestos 
paper  or  brick  in  a  strong  draft  and  ignited  with  a  piece  of 
touch-paper. 

Powdered  stibnite  j  S  flowers  ;  powdered  KNO3 ;  touch-paper. 


ANTIMONY   TRISULPHIDE  277 

8.  Preparation  of  antimony  cinnabar.  —  An  oxysulphide 
of  antimony  of  complex  composition,  possessing  a  beautiful 
color  and  called  antimony  cinnabar,  is  obtained  by  slowly 
heating  a  solution  of  antimony  chloride  with  a  solution  of 
sodium  thiosulphate.  Antimon}^  chloride  solution,  to  which 
the  least  possible  quantity  of  hydrochloric  acid  has  been 
added,  is  mixed  in  a  flask  with  a  solution  of  sodium  thiosul- 
phate and  slowly  heated  with  constant  stirring  to  90°  on  a 
water-bath.    After  a  few  minutes  the  red  precipitate  appears. 

Water-bath  ;  thermometer ;  SbClg  sol.  ;  NagSaOs. 


BORON 


1.  Preparation  of  boron  by  the  reduction  of  boric  anhy- 
dride by  magnesium.  —  Magnesium  powder  reduces  boric 
anhydride  at  a  high  temperature,  forming  magnesium  oxide 
and  amorphous  boron. 

Equal  volumes  of  finely  powdered  magnesium  and  finely 
pulverized  boric  anhydride  are  mixed  in  a  hard-glass  test- 
tube  and  strongly  heated  in  a  blast-lamp.  The  ignition  tube 
should  not  be  more  than  one-fourth  filled  with  the  mixture, 
and  should  be  continually  rotated  while  being  heated. 
Soon  a  temperature  will  be  reached  at  which  the  reaction 
begins,  and  immediately  the  contents  of  the  tube  glow.  The 
tube  is  allowed  to  cool,  is  then  broken,  and  the  contents 
digested  with  pure  dilute  hydrochloric  acid  without  warm- 
ing. The  excess  of  magnesium  and  the  magnesium  oxide 
are  dissolved,  leaving  a  black  powder  of  amorphous  boron, 
which  is  filtered  off  and  allowed  to  dry  on  the  paper. 
Preserve  paper  for  use  in  the  next  experiment. 

B2O3  -f  3  Mg  =  3  MgO  +  2  B. 

Ignition-tube  ;  B2O3  powdered  ;  Mg  powder. 

2.  Combustion  of  boron  in  the  air.  —  Amorphous  boron, 
when  strewn  into  a  Bunsen  flame,  burns  brilliantly.  A 
small  quantity  of  the  amorphous  powder  is  sifted  through 
a  Bunsen  flame  or  blown  through  a  glass  elbow  (Ex.  18,  p.  24) 
into  the  flame. 

278 


BORON 


279 


The  filter-paper,  on  which  the  amorphous  powder  obtained 
in  the  preceding  experiment  was  collected  and  dried,  retains 
a  considerable  quantity  of  the  powder  and,  when  ignited, 
the  particles  of  boron  burn  with  scintillations. 

Glass  elbow;  filter-paper  from  preceding  experiment ;  amorphous  B. 

3.  Preparation  of  boron  trifluoride.  —  Hydrofluoric  acid 
gas  reacts  with  boron  anhydride,  forming  boron  trifluoride. 

Hydrofluoric  acid  gas  is  generated  in  the  presence  of  boric 
anhydride  by  heating  a  mixture  of  24  g.  of  powdered 
calcium  fluoride,  10  g. 
of  powdered  boric  anhy- 
dride, and  20  g.  of  con- 
centrated sulphuric  acid 
in  a  100  cc.  Jena  glass 
Erlenmeyer  flask.  A  one- 
holed  cork,  carrying  a 
glass  elbow,  is  inserted 
in  the  neck  of  the  flask 
and    two    dry    cylinders 

are  arranged  as  in  Fig.  113.  Provision  is  made  for  con- 
ducting the  escaping  gas  into  a  flue.  The  flask  is  then 
gently  heated,  and  the  boron  trifluoride  evolved  soon  expels 
the  air  from  the  flask  and  the  two  cylinders,  and  fumes 
strongly  in  the  air  as  it  escapes  into  the  flue.  The  corks 
are  then  withdrawn  from  the  cylinders,  which  are  quickly 
covered  with  glass  plates. 

H3BO3  -f  3  HF  ^BFg  +  3  H2O. 

Apparatus  (Fig.  113)  ;  100  cc.  Jena  glass  Erlenmeyer  flask;  two 
200  cc.  cylinders  ;  CaF2  powdered  ;  B2O3  powdered. 

4.  Properties  of  boron  trifluoride.  —  A  cylinder  of  the 
gas,  when  opened  to  the  air,  gives  off  dense  white  fumes, 
which  are  acid  to  litmus  paper. 


Fig.  113 


280  CHEMICAL   LECTURE   EXPERIMENTS 

A  cylinder  of  the  gas  is  opened  with  its  mouth  under 
water.  The  gas  is  absorbed,  water  rising  in  the  cylinder 
with  almost  explosive  violence. 

5.  Preparation  of  boric  acid  from  borax.  —  Hydrochloric 
acid  decomposes  sodium  diborate  (borax),  setting  free  boric 
acid,  which,  owing  to  its  insolubility  in  cold  water,  may  be 
easily  crystallized  therefrom. 

Sixty  grams  of  borax  are  dissolved  in  240  cc.  of  boiling 
water,  and  concentrated  hydrochloric  acid  is  added  to  the 
alkaline  solution  until  the  reaction  is  decidedly  acid  to 
litmus.  The  beaker  is  then  immersed  in  a  large  vessel  of 
cold  water,  and  the  boric  acid  on  cooling,  separates  out  in 
large  crystals. 

Na^B^O;  +  2  HCl  4-  5  H2O  =  2  NaCl  +  4  HsBOg. 

Large  vessel  of  cold  water  ;  Na2B407  ;  litmus  paper  (blue). 

6.  Dehydration  of  boric  acid  by  heat.  —  Boric  acid,  when 
strongly  heated  in  a  crucible,  loses  water  and  fuses  to  a 
colorless  anhydride  which  resembles  melted  glass. 

A  platinum  crucible  is  half  filled  with  crystallized  boric 
acid  and  gently  heated  with  a  Bunsen  flame.  Large  quan- 
tities of  water  vapor  are  evolved,  and  on  increasing  the  heat 
the  contents  of  the  crucible  are  fused  to  a  colorless  liquid. 
If  a  glass  rod  dipped  in  the  melted  mass  is  withdrawn,  a 
portion  of  the  liquid  will  adhere  to  it  and  be  drawn  up 
as  a  fine  thread,  which,  on  cooling,  solidifies.  When  cold, 
the  contents  of  the  crucible  become  hard  as  glass  and  are 
best  removed  by  dissolving  in  water. 

2  H3BO3  =  BA  +  3  H2O. 
Pt  crucible  ;  H3BO3. 

7.  Action  of  boric  anhydride  on  water.  —  Twenty-five 
grams  of  powdered  boric  anhydride,  when  mixed  with  30 


BORON 


281 


cc.  of  water,  combine  with  the  water  to  form  boric  acid,  with 
the  liberation  of  great  heat.  An  ether  thermometer,  such  as 
was  shown  in  Fig.  75,  p.  174,  when  thrust  into  the  liquid, 
becomes  so  heated  that  ether  vapor  is  driven  out  of  the  top 
of  the  tube  and  may  there  be  ignited.  Considerable  water 
vapor  escapes  into  the  air  as  a  result  of  the  heat  from  the 
reaction.  ^^q^  +  3  H^O  =  2  H3BO3. 

Ether  thermometer  (Fig.  75,  p.  174)  ;  finely  powdered  B2O3. 

8.  Decomposition  of  sodium  chloride  by  boric   acid. — 

Though  hydrochloric  acid  decomposes  solutions  of  borates 
with  the  liberation  of  boric  acid,  boric  acid  will,  when  fused 
with  sodium  chloride,  drive  off  the  hydrochloric  acid,  form- 
ing sodium  borate.  This  reaction  is  due  to  the  non-volatile 
nature  of  the  boric  acid. 

Equal  volumes  of  fused,  pulverized  so- 
dium chloride  and  powdered  boric  acid 
are  strongly  heated  in  a  crucible.  Water 
is  first  driven  off  from  the  boric  acid,  and 
finally  hydrochloric  acid  fumes  are  evolved. 
The  presence  of  hydrochloric  acid  is  easily 
established  by  blue  litmus  paper  or  a  rod 
moistened  in  strong  ammonium  hydroxide. 

Porcelain  crucible  ;  fused  and  powdered  NaCl ; 
H3BO3  powdered. 

9.  Coloration  of  an  alcohol  flame  by  boric 
acid. — Alcohol,  to  which  a  small  quantity 
of  a  solution  of  boric  acid  has  been  added, 
is  poured  over  some  asbestos  in  an  evapo- 
rating-dish.  On  igniting  the  liquid  it  burns 
with  a  green  flame. 

A  much  larger  flame  may  be  obtained 
by  boiling  the  mixture  of  alcohol  and  boric  Fig.  114 


282  CHEMICAL   LECTURE   EXPERIMENTS 

acid  and  igniting  the  vapor.  Three  grams  of  finely  powdered 
borax  are  mixed  with  3  cc.  of  concentrated  sulphuric  acid 
and  20  cc.  of  ethyl  alcohol  in  a  50  cc.  flask,  fitted  with  a 
one-holed  cork  carrying  a  short  piece  of  glass  tubing  (Fig. 
114).  A  piece  of  combustion  tubing,  10  cm.  long  and  15  to 
20  mm.  in  diameter,  is  vertically  clamped  over  the  small 
glass  tube  through  which  the  vapor  of  alcohol  is  issuing. 
The  alcohol  vapor  mixes  with  air  drawn  in  at  the  lower 
end  of  the  combustion  tube  and  burns,  when  ignited,  in  a 
large  flame  at  the  top  of  the  tube.  The  intense  green  color 
produced  by  the  presence  of  boric  acid  is  strikingly  shown. 

50  cc.  flask ;  cork  and  short  tube ;  10  cm.  length  of  combustion 
tubing;  NaaBiOTj  alcohol. 


SILICON 


SILICON 

1.  Preparation  by  the  reduction  of  silicon  dioxide  by  mag- 
nesium powder.  —  Silicon  dioxide,  when  mixed  with  finely 
powdered  magnesium  and  strongly  heated  in  an  ignition- 
tube,  is  reduced  by  the  magnesium  to  silicon.  In  case  the 
magnesium  is  in  excess,  the  silicon  and  magnesium  unite  to 
form  magnesium  silicide. 

The  reduction  is  w^ell  shown  by  heating  1  g.  of  clean,  dry, 
fine,  white  sand  with  1.5  g.  of  fine  magnesium  powder.  The 
mixture  is  placed  in  a  hard-glass  test-tube,  which  is  gradually 
heated  by  constant  rotation  in  the  flame.  As  the  tempera- 
ture increases,  a  point  will  finally  be  reached  at  which  the 
reaction  starts,  and  it  then  proceeds  throughout  the  whole 
mass,  which  glows  vividly.  The  black  residue  in  the  tube 
consists  chiefly  of  magnesium  silicide. 

The  preparation  of  a  considerable  quantity  of  crude  sili- 
con, which  is  used  in  Ex.  7,  is  easily  accomplished  by  heat- 
ing a  mixture  of  100  g.  of  dry,  fine  sand  with  50  g.  of 
magnesium  power  in  a  Hessian  crucible  over  a  blast-lamp. 
It  is  of  the  greatest  importance  that  the  materials  should  be 
perfectly  dry.  An  asbestos  cover  and  an  iron  plate  should 
be  laid  on  top  of  the  crucible.  The  mixture  is  carefully 
heated,  and  the  reduction,  when  once  started,  proceeds  of 
itself.  This  product,  owing  to  the  deficiency  of  magnesium 
in  the  mixture,  contains  but  a  small  quantity  of  magnesium 

283 


284  CHEMICAL  LECTURE  EXPERIMENTS 

silicide.  After  cooling,  the  product  should  be  treated  with 
dilute  hydrochloric  acid  to  destroy  any  traces  of  magnesium 
silicide  formed,  washed  carefully  with  water,  and  dried  ready 
for  use.  g.Q^  +  2  Mg  =  2  MgO  +  Si. 

Ignition-tube  ;  Hessian  crucible  ;  asbestos  ;  iron  cover  ;  blast-lamp  ; 
fine  sand  ;  fine  Mg  powder. 

2.  Preparation  of  magnesium  silicide.  —  Silicon  dioxide, 
reduced  with  an  excess  of  magnesium,  forms  magnesium 
silicide. 

Twenty  grams  of  magnesium  powder  are  mixed  with  12  g. 
of  fine,  dry  sand  and  heated  over  a  Bunsen  burner  in  an 
iron  saucer.  The  mixture  should  be  covered  with  a  piece  of 
asbestos  paper  to  prevent  the  entrance  of  air.  On  strongly 
heating  with  the  burner  the  reduction  is  completed  and  a 
product  rich  in  magnesium  silicide  is  obtained.  The  material 
should  be  powdered  and  placed  in  a  dry,  tightly  stoppered 
bottle.  4Mg+Si02  =  2MgO  +  SiMg2. 

Iron  saucer;  asbestos  paper';  bottle;  magnesium  powder;  fine, 
dry  Si02. 

SILICON   HYDRIDE 

3.  Preparation  of  silicon  hydride  from  magnesium  silicide 
and  hydrochloric  acid.  —  (a)  Magnesium  silicide  reacts  with 
hydrochloric  acid,  with  the  liberation  of  silicon  hydride,  a 
spontaneously  inflammable  gas. 

A  small  quantity  of  pulverized  magnesium  silicide  is  sifted 
into  10  cc.  of  concentrated  hydrochloric  acid  in  a  50  cc.  cyl- 
inder.   The  gas  liberated  catches  fire  on  exposure  to  the  air. 

The  cylinder  may  be  filled  with  oxygen,  thus  having  an 
atmosphere  of  oxygen  rather  than  air  above  the  hydrochloric 
acid.  The  reaction  on  adding  magnesium  silicide  is  very 
sharp. 


SILICON    HYDRIDE 


285 


(b)  A  considerable  quantity  of  silicon  hydride  may  be 
prepared  and  burned  at  a  jet  by  means  of  the  apparatus, 
Fig.  115.  A  300  cc.  bottle  fitted  with  a  two-holed  rubber 
stopper  is  completely  filled  with  water  and  a  few  grams  of 
magnesium  silicide,  prepared  as  in  the  preceding  experiment, 
are  placed  on  the  bottom.  A  straight  glass 
tube  extends  through  the  cork  nearly  to 
the  bottom  of  the  bottle,  and  is  fitted  by 
means  of  a  cork  to  the  tubulature  of  an 
inverted  500  cc.  bell-jar.  A  glass  elbow, 
inserted  in  the  second  hole  of  the  cork, 
is  connected  by  means  of  a  rubber  tube 
and  pinch-cock  with  a  glass  jet  2  mm. 
internal  diameter.  Twenty  cubic  centi- 
meters of  concentrated  hydrochloric  acid 
are  poured  into  the  bell-jar,  and,  flowing 
down  through  the  straight  glass  tube,  come 
in  contact  with  the  magnesium  silicide.  The  silicon  hydride 
formed  collects  in  the  top  of  the  bottle  and  forces  the  liquid 
up  into  the  bell-jar.  By  carefully  opening  the  pinch-cock 
a  stream  of  silicon  hydride,  mixed  with  some  hydrogen, 
escapes.  On  coming  in  contact  with  the  air  the  gas  sponta- 
neously ignites,  burning  with  a  bright  flame. 

An  iron  plate  held  in  the  upper  part  of  the  flame  becomes 
covered  with  a  white  deposit  of  silicon  dioxide,  one  of  the 
products  of  combustion. 

A  white  porcelain  dish  held  in  the  lower  part  of  the  flame 
is  covered  with  a  brown  deposit  of  amorphous  silicon. 


Fig.  116 


SiMg2  H-  4  HCl  =  2  MgClg  +  SiH,. 
SiH^-f  2  02  =  Si02  +  2H20. 


Apparatus  (Fig.  115);  300  cc.  bottle;  bell-jar;  tubes  and  pinch- 
cock  ;  iron  and  porcelain  dishes  ;  SiMg2. 


286  CHEMICAL   LECTURE   EXPERIMENTS 

(c)  Silicon  hydride  mixed  with  varying  amounts  of  hydro- 
gen (which  for  most  experiments  does  no  harm)  may  easily  be 
obtained  by  using  as  a  generator  a  small  three-necked  Wolff 
bottle,  in  which  the  magnesium  silicide  is  placed  and  cov- 
ered with  water/  Hydrogen  from  the  Kipp  generator 
enters  through  a  glass  elbow,  which  is  thrust  into  one  neck 
of  the  bottle  and  extends  beneath  the  surface  of  the  water. 
A  dropping-funnel  in  the  middle  neck  contains  concentrated 
hydrochloric  acid,  while  the  third  neck  is  provided  with  a 
cork  and  a  delivery-tube.  Hydrogen  is  first  passed  through 
the  apparatus  to  drive  out  all  air,  and  then  concentrated 
hydrochloric  acid  is  allowed  to  fall  upon  the  magnesium 
silicide.  The  silicon  hydride  generated,  mixed  with  con- 
siderable quantities  of  hydrogen,  passes  out  through  the 
delivery-tube  and  ignites  upon  coming  in  contact  with  the 
air.  By  carefully  regulating  the  flow  of  hydrogen  from  the 
Kipp  generator  quite  pure  silicon  hydride  may  be  obtained. 

500  cc.  three-necked  Wolff  bottle  ;  dropping-funnel ;  cork  and  deliv- 
ery-tube ;  H  generator. 

4.  Decomposition  by  heat.  —  Hydrogen  containing  silicon 
hydride  or  the  pure  gas,  silicon  hydride,  is  passed  through 
a  glass  tube,  which  is  strongly  heated.  A  deposition  of 
brown,  amorphous  silicon  is  obtained. 

5.  Combustion  in  the  air.  —  A  cylinder  of  silicon  hydride 
is  collected  over  water,  covered  with  a  glass  plate,  and  placed 
mouth  upwards  on  the  table.  On  removing  the  plate,  the 
gas  ignites  of  itself  and  burns.  Owing  to  the  deficiency  of 
air,  a  deposit  of  brown  amorphous  silicon  is  left  on  the 
inside  of  the  cylinder. 

6.  Explosion  with  air  or  oxygen,  —  Air  or  oxygen,  when 
allowed  to  enter  a  confined  volume  of  silicon  hydride,  pro- 
daces  an  explosion. 


SILICON   TETRACHLORIDE 


287 


Twenty  cubic  centimeters  of  silicon  hydride  are  collected  in 
a  100  cc.  cylinder,  and  one  or  two  bubbles  of  air  are  allowed 
to  rise  inside  the  cylinder.     A  sharp  explosion  is  obtained. 

If  oxygen  is  admitted  to  a  confined  volume  of  the  hydride, 
the  greatest  care  must  be  exercised  that  not  more  than  one 
bubble  is  introduced  at  a  time. 

The  conditions  of  this  experiment  may  be  reversed  and  a 
bubble  of  silicon  hydride  allowed  to  enter  a  confined  volume 
of  air  or  oxygen.  The  introduction  of  silicon  hydride  is 
best  made  from  the  apparatus  of  Fig.  115,  p.  285,  which 
admits  of  a  careful  regulation  of  the  flow  of  the  gas. 

Pneumatic  trough  ;  cylinders ;  O  supply  ;  SiH4  supply. 


SILICON   TETRACHLORIDE 

7.   Preparation  by  the  action  of  chlorine  on  crude  silicon.  — 

A  quantity  of  dry,  crude  silicon,  prepared  as  in  Ex.  1,  is  placed 


Fig.  116 


in  a  50  cm.  length  of  combustion  tubing,  through  which  dry 
chlorine  is  conducted  (Fig.  116).     As  the  quantity  of  silicon 


288  CHEMICAL   LECTURE   EXPERIMENTS 

tetrachloride  formed  varies  greatly  with  the  temperature, 
it  is  necessary  to  heat  the  tube  in  an  air-bath  consisting  of 
a  tin  or  sheet-iron  trough  covered  with  a  piece  of  asbestos 
paper.  A  thermometer  is  placed  in  the  air-bath,  which 
should  be  heated  by  means  of  a  four-tube  burner  to  345°  C. 
The  issuing  gas  is  conducted  through  a  U-tube  immersed  in 
ice-water,  and  the  silicon  tetrachloride  condenses  to  a  light 
yellow  liquid. 

Si  -f  2  CI,  =  SiCl4. 

50  cm.  length  combustion  tubing ;  air-bath  ;  four-tube  burner  ;  ther- 
mometer ;  U-tube  immersed  in  ice- water ;  CI  generator  (Fig.  39, 
p.  81)  ;   crude  silicon  from  Ex.  1. 

8.  Decomposition  by  moisture.  —  (a)  Silicon  tetrachloride 
fumes  strongly  in  the  air,  from  which  it  abstracts  moisture. 
The  reaction  is  accompanied  by  a  liberation  of  hydrochloric 
acid  and  a  white  powder  consisting  of  silicic  acid  remains.  A 
few  cubic  centimeters  of  the  liquid  are  poured  into  a  glass 
crystallizing  dish  and  are  allowed  to  stand  exposed  to  the 
air.  A  piece  of  moist  blue  litmus  paper  is  immediately  red- 
dened when  exposed  to  the  fumes.  When  the  reaction  is 
complete,  a  white  powder  is  left  in  the  bottom  of  the  dish. 

Glass  crystallizing  dish  ;  litmus  paper  (blue)  ;  SiCU. 

(b)  Silicon  tetrachloride  unites  directly  with  water,  form- 
ing hydrochloric  acid  and  gelatinous  silicic  acid. 

A  few  drops  of  the  tetrachloride  are  allowed  to  fall  into 
2  cc.  of  water  in  a  test-tube.  Gelatinous  silicic  acid  is 
formed  and  hydrochloric  acid  escapes. 

SiCl4  -f  4  HgO  =  H4Si04  +  4  HCl. 


SILICON    TETRAFLUORIDE  289 

SILICON     TETRAFLUORIDE     AND      HYDRO- 
FLUOSILICIC   ACID 

9.  Preparation  of  silicon  tetrafluoride.  —  When  hydro- 
fluoric acid  gas  is  generated  in  the  presence  of  silicon 
dioxide,  silicon  tetrafluoride  is  formed. 

Thirty  grams  of  finely  pulverized  calcium  fluoride  are 
mixed  with  an  equal  weight  of  fine  sand  and  heated  with 
sufficient  concentrated  sulphuric  acid  to  make  a  thin  paste. 
The  mixture  is  placed  in  a  250  cc.  flask  fitted  with  a  two- 
holed  rubber  stopper.  A  double  safety-funnel,  such  as  is 
shown  in  Fig.  85,  p.  196,  containing  mercury,  is  placed  in 
one  hole  of  the  stopper,  and  the  issuing  gas  is  conducted 
through  a  glass  elbow  in  the  second  hole  to  the  bottom  of  a 
dry  400  cc.  cylinder  arranged  as  in  Fig.  113,  p.  279.  Two 
cylinders  are  placed  in  series  and  filled  with  the  dry  gas  by 
gently  heating  the  flask. 

Si02  +  4  HF  =  SiF,  +  2  HgO. 

250  cc.  flask  ;  two-holed  rubber  stopper  ;  safety-funnel ;  two  400  cc. 
dry  cylinders  ;  fine  Si02  ;  finely  pulverized  CaF2  ;  Hg. 

10.  Silicon  tetrafluoride  is  a  non-supporter  of  combustion.  — 

A  burning  candle  thrust  into  a  jar  of  silicon  tetrafluoride  is 
immediately  extinguished.     The  gas  itself  does  not  burn. 

Candle  on  wire  ;  jar  of  SiF4. 

1 1 .  Decomposition  of  silicon  tetrafluoride  by  water  vapor. — 

Silicon  tetrafluoride  is  decomposed  by  the  action  of  water, 
forming  hydrofluosilicic  and  silicic  acids.  A  jar  of  silicon 
tetrafluoride,  when  opened  in  moist  air,  fumes  strongly. 

A  glass  rod  moistened  with  water,  when  lowered  into  a 
jar  of  the  gas,  will  become  covered  with  a  deposit  of  white 
silicic  acid. 


290    •    .        CHEMICAL   LECTURE    EXPERIMENTS 

If  silicon  tetrafluoride  is  slowly  conducted  into  the  lower 
end  of  a  yertically  clamped  piece  of  combustion  tubing  60  cm. 
long,  the  decomposition  of  the  gas  by  water-vapor  may  be 
more  strikingly  shown.  Moisture  should  be  introduced  into 
the  combustion  tube  just  before  use  by  blowing  through  it 
with  the  mouth.  As  the  gas  slowly  rises  in  the  tube,  the 
walls  become  covered  with  a  white  deposit  of  silicic  acid. 

60  cm.  length  of  combustion  tube  ;  jars  of  SiF4  ;  SiF4  supply. 

12.  Preparation  of  hydrofluosilicic  acid  by  the  action  of 
silicon  tetrafluoride  on  water.  —  Silicon  tetrafluoride  is  con- 
ducted into  water,  and,  to  prevent  the  stoppage  of  the  tube 
by  the  silicic  acid  formed,  the  end  should  dip  under  a 
2  cm.  layer  of  mercury.  The  mercury  may  also  be  placed 
in  a  small  crucible  in  the  bottom  of  the  cylinder.  As  each 
bubble  of  gas  rises  through  the  water  it  becomes  coated  with 
a  film  of  silicic  acid,  which  collects  as  a  froth  on  the  surface 
of  the  water. 

3  SiF4  +  4  H2O  =  H4Si04  +  2  H.SiFe. 
200  cc.  cylinder  ;  small  porcelain  crucible  ;  SiF4  supply  ;  Hg. 


CARBON 


CARBON 


1.  Preparation  of  charcoal  by  heating^  organic  material 
out  of  contact  with  the  air.  —  Organic  material,  when  heated 
out  of  contact  with  the  air,  loses  a  great  part  of  its  water 
and  becomes  converted  to  charcoal. 

(a)  A  few  small  pieces  of  wood  are  placed  in  the  bottom 
of  a  small  Hessian  crucible,  covered  with  a  layer  of  fine 
sand,  and  strongly  heated  till  no  more  fumes  are  given  off. 
The  combustible  nature  of  the  gases  evolved  may  be  shown 
by  igniting  them.  The  crucible  is  allowed  to  become  cool, 
the  sand  is  shaken  out,  and  the  small  pieces  of  charcoal 
removed.  The  great  shrinkage  in  the  wood  may  be  shown 
by  having  a  number  of  pieces  of  wood  of  the  same  size,  of 
which  only  a  part  are  heated. 

(b)  Sugar  may  be  charred  in  a  porcelain  crucible  and  the 
carbonaceous  residue  exhibited. 

(c)  In  the  dry  distillation  of  wood  (Ex.  61,  p.  324),  the 
residue  of  charcoal  may  be  removed  from  the  tube. 

Hessian  crucible  ;  porcelain  crucible  ;  sand  ;  small  pieces  of  wood  ; 
sugar. 


2.  The  electrical  conductivity  of  carbon.  —  The  electrical 
conductivity  of  the  various  forms  of  carbon  may  be  shown 
by  closing  an  electric  circuit  with  a  piece  of  charcoal,  a  bit 

291 


292 


CHEMICAL  LECTURE   EXPERIMENTS 


of  electric-light  carbon,  a  pencil  sharpened  at  both  ends,  and 
a  piece  of  graphite.  A  fine  piece  of  iron  wire  or  a  piece  of 
platinum  wire,  such  as  is  used  in  suspending  Welsbach 
mantles,  connects  the  two  upright  wires  shown  in  Fig.  22, 
p.  53.  Four  or  five  cells  of  a  bichrornate  battery  are  con- 
nected with  the  terminals  of  these  wires,  leaving  a  gap  in 
the  circuit  which  can  be  closed  by  the  carbon  conductors. 
On  closing  the  circuit,  the  platinum  wire  will  be  heated  to 
redness  or  even  melted,  while  the  iron  wire,  if  used,  will  be 
ignited  and  burn  in  the  air.  The  circuit  between  a  dry  bat- 
tery and  an  electric  bell  may  be  used  in  place  of  the  platinum 
wire  and  large  battery. 

Wires  ou  block  (Fig.  22,  p.  53)  ;  bichromate  battery  ;  fine  Fe  or  Pt 
wire ;  pieces  of  charcoal ;  electric-light  carbon  rod ;  lead-pencil  ; 
graphite. 

3.   The  absorption  of  hydrogen  sulphide  by  charcoal. — 

(a)  Air  from  a  water-blast  or  gasometer  is  conducted 
through  a  gas  washing-bottle  one-third  tilled  with  a  strong 
aqueous  solution  of  hydrogen  sulphide.  A  T-tube  connects 
the  gas  washing-bottle  with  an  80  cm.  length  of  combustion 


m 


^31]=^ 


... 


Fig.  117 


tubing  filled  with  coarsely  pulverized  charcoal.  The  stem 
of  the  T-tube  is  connected  by  means  of  a  short  piece  of  rub- 
ber tubing  and  a  pinch-cock  with  a  glass  tube  dipping  into 
a  dilute  solution  of  lead  acetate  in  a  beaker  (Fig.  117).  The 
other  end  of  the  combustion  tube  is  provided  with  a  cork  and 
a  glass  elbow  dipping  into  a  beaker  containing  lead  acetate 


CARBON  293 

solution.  By  opening  the  pinch-cock  and  closing  the  end  of 
the  combustion  tube,  the  air  containing  hydrogen  sulphide  is 
caused  to  bubble  through  the  lead  acetate  solution,  produc- 
ing a  black  precipitate.  On  closing  the  pinch-cock,  the  air 
and  hydrogen  sulphide  proceed  through  the  combustion-tube 
filled  with  charcoal,  and  then  bubble  through  the  lead  acetate 
solution  in  the  beaker  at  the  end  of  the  combustion-tube. 
Here  it  will  be  observed  that  no  discoloration  will  take  place, 
as  all  the  hydrogen  sulphide  has  been  absorbed  by  the  char- 
coal. The  rate  at  which  the  air  is  conducted  through  the  sys- 
tem should  not  be  too  fast  to  admit  of  counting  the  bubbles. 

Gas  washing-bottle  ;  80  cm.  length  of  combustion  tubing ;  current 
of  air  ;  H2S  solution  ;  coarsely  pulverized  charcoal. 

(b)  Bone-black  absorbs  gases  from  their  solution  in  water 
as  well  as  from  air,  and  if  a  weak  solution  of  hydrogen  sul- 
phide is  shaken  with  an  excess  of  bone-black  and  then  filtered, 
it  will  be  found  that  the  filtrate  will  no  longer  smell  of  the 
gas  nor  give  any  of  its  reactions. 

H2S  solution  ;  bone-black. 

4.  Absorptive  power  of  carbon  for  coloring  matter.  — 

The  use  of  finely  divided  carbon,  especially  in  the  form  of 
bone-black,  in  decolorizing  liquids  is  shown  by  boiling  50  cc. 
of  litmus  solution  with  10  g.  of  bone-black.  On  filtering  off 
the  bone-black,  the  filtrate  will  be  found  to  be  colorless. 

If  double  the  quantity  of  bone-black  is  used  and  the  flask 
is  vigorously  shaken,  the  application  of  heat  is  unnecessary. 

The  bone-black  may  be  placed  in  a  vertically  clamped 
wide  glass  tube  having  a  layer  of  asbestos  next  the  one-holed 
cork  in  the  lower  end.  If  litmus  solution  is  allowed  to  per- 
colate slowly  through  the  long  layer  of  bone-black,  the  color 
is  discharged. 

40  cm.  length  tubing  (15  mm.  diameter);  asbestos;  bone-black; 
litmus  solution. 


294  CHEMICAL  LECTURE  EXPERIMENTS 

5.   Absorption  of  salts  from  their  solutions  by  bone-black.  — 

Finely  divided  carbon  removes  salts,  as  well  as  coloring  mat- 
ters, from  solutions,  as  can  be  seen  by  boiling  100  cc.  of  a 
solution  of  lead  nitrate  containing  .5  g.  of  salt  to  the  liter 
with  10  g.  of  animal  charcoal.  On  filtering  off  the  liquid, 
the  addition  of  a  solution  of  hydrogen  sulphide  to  the  clear 
filtrate  will  produce  no  precipitate,  while  the  original  solu- 
tion will  yield,  on  the  addition  of  hydrogen  sulphide,  a 
black  precipitate  of  lead  sulphide. 

A  solution  of  acid  sulphate  of  quinine  possessing  a  de- 
cidedly bitter  taste  may  be  similarly  treated  with  animal 
charcoal,  and  afterward  the  filtrate  will  no  longer  taste  of 
quinine. 

.5  g.  Pb(N03)2  in  1  1.  of  water;  bone-black ;  acid  sulphate  of  qui- 


6.  Combustion  of  graphite  in  oxygen.  —  In  spite  of  the 
great  fire-resisting  properties  of  graphite,  it  will,  when 
heated  to  a  sufficiently  high  temperature,  burn  in  an 
atmosphere  of  oxygen  to  form  carbon  dioxide. 

A  small  piece  of  pipe-stem  or  fire-brick  is  fastened  to  a 
piece  of  stout  wire,  which  is  in  turn  fastened  to  a  cork.  A 
hollow  should  be  made  in  the  brick,  by  means  of  a  file  and 
a  small  piece  of  graphite  laid  in  it.  By  directing  a  jet  of 
oxygen  through  a  glass  tube,  held  in  a  small  gas  or  candle 
flame,  sufficient  heat  will  be  developed  to  ignite  the  graphite. 
When  glowing  strongly  in  the  air,  the  graphite  is  lowered 
into  a  wide-necked  flask  filled  with  oxygen  by  displace- 
ment, where  it  will  continue  to  glow  and  burn  to  carbon 

dioxide.  _ 

C  -f  O2  =  CO2. 

200  cc.  flask  (wide- necked)  ;  fire-brick  or  pipe-stem ;  stout  wire ; 
O  supply ;  graphite. 


CARBON  295 

7.  Combustion  of  a  diamond  in  oxygen.  —  Diamond,  like 
other  forms  of  carbon,  when  heated  strongly,  burns  in 
oxygen  to  form  carbon  dioxide. 

A  piece  of  pipe-stem,  1  cm.  long,  is  hollowed  a  little 
in  one  end  with  a  file  and  the  hole  plugged  with  a  piece 
of  asbestos  paper.  A  copper  wire  is  bent  like  a  hook 
and  the  pipe-stem  fitted  on  the  end.  The  wire  is  fastened 
to  a  cork  fitting  a  250  cc.  wide-mouthed  flask  filled  with 
oxygen,  and  is  cut  at  such  a  length  that  when  the  cork  rests 
in  the  neck  of  the  flask  the  bend  in  the  wire  nearly  touches 
the  bottom.  The  diamond  ^  is  placed  in  the  hollow  in  the 
upper  end  of  the  pipe-stem  and  heated  to  incandescence  with 
a  small  gas  flame,  through  which  a  gentle  current  of  oxygen 
is  directed  (Fig.  118).  The  table  should  be 
covered  with  a  large  piece  of  glazed  paper, 
such  as  is  used  in  transferring  precipitates, 
to  catch  the  diamond  in  case  it  should  be 
shaken  off  the  wire.  When  the  diamond  is 
strongly  glowing,  the  gas  flume  may  be  ex- 
tinguished and  the  stream  of  oxygen  allowed 
to  play  upon  it.  The  combustion  is  very 
vivid.  The  oxygen  stream  should  then  be 
cut  off  and  the  diamond  allowed  to  cool  in  Fig.  118 
the  air.  It  will  be  seen  that  the  glowing 
almost  immediately  stops.  On  again  heating  the  diamond 
and  lowering  it  into  the  flask  of  oxygen,  it  will  glow  for 
some  little  time,  and  the  presence  of  carbon  dioxide  in  the 
flask  may  be  established  by  adding  20  cc.  of  a  solution  of 
barium  hydroxide  and  shaking  the  flask.  A  precipitate  of 
barium  carbonate  will  be  formed. 

1  Small  crystals  of  diamond,  with  the  longer  axis  approximately 
2  mm.  long,  maybe  obtained  of  George  L.  English  &  Co.,  3  and  5  West 
18th  St.,  New  York  City,  at  a  cost  of  25  cents  per  crystal.  Crystals 
of  this  size  and  cost  have  been  used  by  the  writer  and  are  large  enough 
to  give  good  results  in  this  experiment. 


296  CHEMICAL   LECTURE   EXPERIMENTS 

To  prevent  the  possible  introduction  of  carbon  dioxide 
into  the  flask  from  the  flame  used  in  heating  the  diamond, 
it  is  best  to  cut  off  the  gas  supply  and  allow  the  diamond  to 
glow  in  the  jet  of  pure  oxygen  a  moment  before  lowering  it 
into  the  flask.  The  flask  should  be  filled  with  oxygen  by 
displacement,  in  order  to  avoid  wetting  the  interior. 

250  cc.  wide-mouthed  flask  ;  wire  and  pipe-stem  ;  O  jet ;  small  crys- 
tal or  fragment  of  diamond  ;  Ba(0H)2  sol. 

8.  Oxidation  of  carbon  at  low  temperatures.  —  The  oxida- 
tion of  carbon  at  the  temperature  of  the  room  is  interestingly 
shown  by  electrolyzing  dilute  sulphuric  acid  in  an  electro- 
lytic apparatus,  using  carbon  electrodes  (Ex.  24,  p.  95).  It 
will  be  found  that,  while  there  is  a  very  vigorous  evolution 
of  hydrogen  from  the  negative  pole,  there  will  be  very  little, 
if  any,  gas  ascend  from  the  positive  pole.  If  the  two  elec- 
trodes are  carefully  filed  and  rubbed  with  emery  paper 
before  the  experiment,  the  positive  electrode  will  be  found 
to  be  considerably  corroded,  while  the  negative  electrode 
will  appear  unacted  upon.  The  disintegration  of  the  posi- 
tive electrode  is  further  made  apparent  by  the  presence  of 
small  particles  of  carbon  in  the  liquid  and  on  the  rubber 
stopper  holding  the  electrode. 

Electrolytic  apparatus  (Fig.  46,  p.  95),  with  carbon  electrodes; 
10  per  cent  H2SO4 ;  battery. 

CARBON   MONOXIDE 

PREPARATION 

9.  From  carbon  dioxide  and  carbon.  —  Carbon  dioxide, 
when  passed  over  heated  carbon,  becomes  reduced  to  car- 
bon monoxide. 

Coarsely  pulverized  charcoal  is  placed  in  a  30  cm.  length 
of  combustion-tubing,  and  a  gentle  current  of  dry  carbon 


CARBON   MONOXIDE 


297 


dioxide  is  conducted  through  the  tube,  which  is  strongly- 
heated  with  a  four-tube  burner  (Fig.  119).  The  issuing  gas 
is  conducted  through  a  U-tube  containing  soda-lime,  and 
issues  through  a  vertical  piece  of  glass  tubing,  which  serves 


>c=[|[i     r-1  .gSggL»:^.'^4^§^:Sg)'&Q     cj  |)=Q=^ 


as  a  jet.  The  gas  issuing  from  the  jet,  when  ignited,  burns 
with  a  blue  fliame.  The  gas  may  be  collected  in  cylinders 
at  the  pneumatic  trough.  A  large  flame  is  obtained  by  fill- 
ing a  liter  cylinder  with  the  gas  and,  after  igniting  it, 
pouring  water  rapidly  into  the  cylinder. 

CO2  +  C  =  2  CO. 

30  cm.  length  combustion-tubing ;  4-tube  burner  ;  liter  cylinder ; 
soda-lime  ;  U-tube  ;  CO2  generator ;  charcoal. 


10.  From  carbon  dioxide  and  zinc.  —  Zinc  dust  at  a  low 
red  heat  effects  the  reduction  of  carbon  dioxide  to  carbon 
monoxide. 

A  Jena  glass  combustion-tube  is  filled,  for  about  30  cm. 
of  its  length,  with  a  layer  of  zinc  dust,  over  which  a  current 
of  carbon  dioxide  is  passed.  A  cork,  carrying  a  glass  elbow 
which  serves  as  a  jet,  is  inserted  in  the  other  end  of  the  tube. 
On  gradually  heating  the  tube  with  a  four-tube  burner, 
the  reduction  begins,  and  soon  sufficient  carbon  monoxide 


298  CHEMICAL  LECTURE  EXPERIME:NTS 

will  issue  from  the  jet  to  be  lighted  and  continue  to  burn. 
At  the  end  of  the  operation  it  will  be  seen  that  a  portion  of 
the  zinc  dust  has  been  converted  to  white  zinc  oxide. 

CO2  +  Zn  =  ZnO  +  CO. 

Jena  glass  combustion-tube ;  CO2  generator  ;  4-tube  burner ;  Zn 
dust. 

11.  By  the  action  of  sulphuric  acid  on  oxalic  acid.  —  Sul- 
phuric acid  reacts  with  oxalic  acid  to  form  equal  volumes  of 
carbon  monoxide  and  carbon  dioxide. 

Thirty  grams  of  crystallized  oxalic  acid  are  placed  in  a 
liter  flask  and  mixed  with  100  cc.  of  concentrated  sulphuric 
acid.  The  flask  is  provided  with  a  two-holed  cork  carry- 
ing a  long  thistle-tube  and  a  delivery-tube  connected  with 
a  gas  washing-bottle.  The  contents  of  the  flask  are  gen- 
tly heated,  and  the  evolution  of  the  gas  is  controlled  by 
the  application  of  heat.  The  liberated  gas  is  conducted 
through  a  strong  solution  of  potassium  hydroxide  in  a  gas 
washing-bottle,  to  deprive  it  of  the  greater  portion  of  carbon 
dioxide.  A  U-tiibe  filled  with  soda-lime,  connected  to  the 
exit  tube  of  the  gas  washing-bottle,  removes  the  last  traces 
of  carbon  dioxide,  and  the  pure  carbon  monoxide  may  be 
ignited  at  a  glass  jet.  The  apparatus  is  identical  with  that 
shown  in  Fig.  120,  save  that  the  thermometer  there  shown 
IS  not  used.         ^^^  A  =  CO^  +  CO  -f-  H.O. 

Liter  flask  ;  thistle-tube  ;  delivery-tube ;  gas  washing-bottle ; 
U-tube  ;  soda-lime  ;  H2C2O4  ;  KOH. 

12.  By  the  action  of  sulphuric  acid  on  potassium  fer- 
rocyanide.  —  The  complex  reaction  between  sulphuric  acid 
and  potassium  ferrocyanide  furnishes  a  ready  means  of 
obtaining  pure  carbon  monoxide,  and  for  preparing  this  gas 
in  large  quantities  on  the  lecture-table  this  method  is  by  far 
the  best. 


CARBON    MONOXIDE 


299 


Forty-five  grams  of  pulverized  potassium  ferrocyanide  are 
mixed  with  300  cc.  of  concentrated  sulphuric  acid  in  a  2  1. 
flask.  The  flask  is  closed  with  a  three-holed  rubber  stop- 
per, carrying  a  thistle-tube  extending  below  the  liquid  in 
the  flask,  a  glass  elbow,  and  a  thermometer,  the  bulb  of 
which  is  immersed  in  the  liquid.  Care  should  be  taken 
to  have  that  portion  of  the  thermometer  reading  between 
150°  and  175°  uncovered  by  the  cork.  The  issuing  gas  is 
conducted  through  a  gas  washing-bottle  containing   potas- 


FiG.  120 


sium  hydroxide,  followed  by  a  U-tube  containing  soda-lime 
(Fig.  120).  The  flask  is  gradually  heated  and  the  tempera- 
ture maintained  at  170°,  where  a  very  regular  evolution  of 
the  gas  will  be  obtained.  The  pure  gas  issuing  from  the 
soda-lime  tube  may  be  ignited  or  collected  in  jars  at  the 
pneumatic  trough,  for  use  in  any  of  the  experiments 
described  beyond.  On  removing  tlie  flame  and  allowing 
the  contents  of  the  flask  to  cool,  the  evolution  of  gas  ceases. 
By  heating  the  mixture  again  to  170°,  even  after  long  stand- 


300  CHEMICAL   LECTURE   EXPERIMENTS 

ing,  a  steady  evolution  of  carbon  monoxide  is  obtained.  If 
the  temperature  is  not  allowed  to  rise  above  175°,  no  diffi- 
culty in  the  preparation  of  the  gas  by  this  method  vrill  be 
experienced. 

2  1.  flask;  thistle-tube;  elbow;  thermometer;  soda-lime;  U-tube  ; 
pulverized  K4FeCy6. 

13.  Preparation  of  water  gas  by  the  action  of  steam  on 
hot  charcoal.  —  By  passing  steam  over  glowing  charcoal, 
the  water  vapor  becomes  partially  reduced  by  the  carbon, 
and  a  mixture  of  hydrogen  and  carbon  monoxide,  i.e.,  water 
gas,  issues  from  the  tube. 

A  combustion-tube  is  prepared  in  a  manner  similar  to 
that  described  for  the  decomposition  of  nitric  acid  (Ex.  79, 
p.  226).  The  tube  is  filled  with  fine  lumps  of  charcoal, 
which  are  strongly  heated  by  means  of  a  four-tube  burner. 
Steam,  generated  in  the  apparatus  described  in  Ex.  2, 
p.  41,  is  conducted  through  a  glass  tube,  surrounded  with 
a  roll  of  asbestos  paper  inserted  in  one  end  of  the  combustion- 
tube,  which  prevents  the  deposition  of  water  and  subsequent 
fracture  of  the  tube.  If  the  issuing  gas  is  collected  at  the 
pneumatic  trough,  it  will  be  found  to  be  combustible. 

H2O  +  C  =  CO  +  H2. 

Combustion-tube  surrounded  with  wire  gauze  (Ex.  79,  p.  226)  ; 
asbestos  paper ;  steam  generator  (Ex.  2,  p.  41)  ;  4-tube  burner ; 
charcoal. 

PROPERTIES 

14.  Influence  of  moisture  upon  the  combustion  of  carbon 
monoxide  in  the  air.  —  Carbon  monoxide,  dried  by  passing 
through  a  U-tube  containing  pumice-stone  drenched  with 
sulphuric  acid,  will  burn  in  the  air;  but  if  the  jet  is  low- 
ered into  a  cylinder  containing  dry  air,  the  flame  will  be 
extinguished. 

Twenty-five  cubic  centimeters  of  concentrated  sulphuric 


CARBON   MONOXIDE  301 

acid  are  poured  into  a  500  cc.  glass-stoppered  wide-mouthed 
specimen  bottle,  and  the  air  is  thoroughly  dried  by  care- 
fully shaking  the  well-stoppered  bottle.  A  current  of  carbon 
monoxide,  dried  in  the  manner  described,  is  allowed  to 
burn  from  a  recurved  jet.  On  removing  the  stopper  of 
the  specimen  bottle  and  lowering  the  jet  into  the  jar,  the 
flame  will  be  extinguished.  The  gas  should  be  passed 
through  solid  absorbents  for  carbon  dioxide  and  water  to 
prevent  the  flickering  of  the  flame  caused  by  the  bubbling 
of  the  gas  through  a  liquid.  A  U-tube  filled  with  soda-lime 
and  a  similar  tube  containing  pumice-stone  and  sulphuric 
acid  will  effectively  purify  and  dry  the  gas. 

500  cc.  glass-stoppered  wide-mouthed  specimen  bottle ;  recurved 
jet  (Fig.  41,  p.  85);  CO  supply. 

15.  Explosion  of  a  mixture  of  carbon  monoxide  and  oxy- 
gen.—  A  mixture  of  2  volumes  of  carbon  monoxide  and 
1  volume  of  oxygen  explodes  with  considerable  violence. 

A  100  cc.  cylinder  is  two-thirds  filled  with  carbon  monox- 
ide ahd  the  remaining  third  with  oxygen.  The  mouth  of 
the  cylinder  should  be  covered  with  a  piece  of  cardboard 
having  an  8  mm.  hole  in  the  centre.  The  cylinder  should 
be  removed  from  the  pneumatic  trough,  placed  mouth 
upward  on  the  table,  and  the  flame  applied  at  the  hole  in 
the  cardboard.  The  explosion  is  quite  sharp,  blowing  the 
cardboard  into  the  air. 

The  explosive  gaseous  mixture  may  also  be  made  in  a 
round-bottomed  ginger-ale  bottle,  as  in  Ex.  30,  p.  67,  and 
there  exploded. 

100  cc.  cylinder  ;  cardboard  with  hole  in  centre ;  ginger-ale  bottle  ; 
CO  supply  ;  O  supply. 

16.  Absorption  by  cuprous  chloride.  —  (a)  A  hydrochloric 
acid  solution  of  cuprous  chloride  absorbs  carbon  monoxide 
readily. 


302  CHEMICAL  LECTURE  EXPERIMENTS 

A  quantity  of  the  gas  is  collected  in  the  eudiometer 
(Fig.  11,  p.  26),  and  an  acid  solution  pf  cuprous  chloride 
is  allowed  to  flow  down  through  it.  If  no  impurities  are 
present,  the  gas  will  be  completely  absorbed. 

(b)  The  absorption  of  this  gas  in  cuprous  chloride  solution 
may  also  be  shown  by  conducting  the  gas  through  a  series 
of  three  wash-bottles,  the  middle  one  of  which  contains  the 
cuprous  chloride  solution,  the  others  containing  water.  The 
wash-bottles  are  not  more  than  a  third  filled  with  liquid. 
If  a  current  of  carbon  monoxide  is  passed  through  the 
system,  the  difference  in  the  rate  of  bubbling  in  the  first 
and  last  bottles  will  be  very  apparent.  On  heating  the 
solution,  carbon  monoxide  is  again  liberated. 

Eudiometer  (Fig.  11,  p.  26);  3  gas  washing-bottles;  CO  supply; 
CU2CI2  in  HCl. 

17.  Action  on  an  ammoniacal  solution  of  silver  nitrate.  — 

Carbon  monoxide  reduces  an  alkaline  solution  of  silver. 

A  gentle  current  of  the  gas,  when  conducted  through  a 
solution  of  silver  nitrate,  to  which  a  slight  excess  of 
ammonium  hydroxide  has  been  added,  produces  a  black 
precipitate  of  metallic  silver. 

CO  supply  ;  AgNOs  solution. 

18.  Action  on  palladious  chloride.  —  Carbon  monoxide 
reduces  solutions  of  palladious  chloride  to  black  metallic 
palladium. 

A  paper  moistened  with  palladious  chloride  solution  fur- 
nishes a  delicate  test  for  carbon  monoxide,  for,  when  held 
in  this  gas,  it  is  immediately  blackened. 

CO  supply  ;  PdCl2  solution. 

19.  Reduction  of  palladious  chloride  by  a  cuprous  chloride 
solution  of  carbon  monoxide.  —  The  delicacy  of  the  reaction 


CARBON   DIOXIDE  303 

between  carbon  monoxide  and  palladious  chloride  is  shown 
by  adding  3  drops  of  a  cuprous  chloride  solution  of  carbon 
monoxide  to  400  cc.  of  water  in  a  beaker.  One  drop  of  pal- 
ladious chloride  solution  is  added  with  thorough  stirring. 
In  a  few  moments  the  contents  of  the  beaker  become  a  deep 
black  from  the  precipitated  palladium. 

CO  dissolved  in  CU2CI2  solution  ;  PdCl2  solution. 

20.  Reduction  of  a  solution  of  iodic  acid.  —  A  current  of 
carbon  monoxide,  conducted  into  a  warm  solution  of  iodic 
acid,  reduces  the  acid,  forming  carbon  dioxide  and  liberating 
iodine. 

A  solution  of  iodic  acid  is  gently  heated  in  a  beaker,  and 
a  current  of  carbon  monoxide  is  allowed  to  bubble  through 
the  liquid.  A  filter-paper  moistened  with  starch  solution 
and  held  above  the  liquid  is  turned  blue  by  the  iodine 
liberated  and  vaporized. 

CO  supply ;  HIOs  solution ;  starch  solution. 

CAEBON   DIOXIDE 

PREPARATION 

21.  Combustion  of  charcoal  in  a  confined  volume  of  oxygen. 
Volumetric  relation  of  the  carbon  dioxide  to  the  oxygen  con- 
sumed. —  Carbon  burns  in  oxygen  to  form  1  volume  of  car- 
bon dioxide  for  every  volume  of  oxygen  used.  If  charcoal 
is  burned  in  a  confined  volume  of  oxygen,  the  volume  of  the 
product  will  be  the  same  as  that  of  the  oxygen  consumed ; 
hence  there  will  be  no  difference  in  pressure  in  the  interior 
of  the  vessel  at  the  end  of  the  combustion. 

The  apparatus  used  for  this  experiment  is  that  shown  in 
Fig.  68,  p.  150,  A  6  mm.  piece  of  charcoal,  preferably  that 
used  in  blowpipe  work,  is  placed  on  a  platinum   spoon, 


304 


CHEMICAL   LECTURE   EXPERIMENTS 


ignited  in  the  air,  and  thrust  into  the  flask  previously  filled 
with  oxygen.  The  heat  of  the  burning  carbon  expands  the 
gases  and  causes  the  mercury  to  rise  in  the  open  arm  of  the 
U-tube.  After  the  operation  is  completed  and  the  flask  has 
regained  its  normal  temperature,  the  level  of  the  mercury  in 
the  arms  of  the  U-tube  will  be  found  to  be  the  same. 

Apparatus  (Fig.  68,  p.  160);   700  cc.  Jena  glass  distilling  flask; 
U-tube  ;  Hg ;  charcoal. 

22.  Preparation  from  magnesite  by  heat.  —  A  thick-walled 
test-tube  is  partially  tilled  with  5  or  10  g.  of  magnesite  such 
as  is  used  for  analysis.  A  cork 
with  a  delivery-tube  dipping  into 
a  glass  cylinder  containing  lime- 
water  is  inserted  in  the  mouth  of 
the  test-tube,  which  is  then  clamped 
in  an  inclined  position  (Fig.  121). 
On  heating  the  magnesite,  consider- 
able quantities  of  carbon  dioxide 
are  given  off  and  produce  a  marked 
cloudiness  in  the  lime-water. 

MgO  -f-  CO2. 


Fig.  121 


MgC03 
Hard-glass  test-tube  ;  magnesite  ;  lime-water. 


23.  From  calcium  carbonate  and  hydrochloric  acid.  —  By 

far  the  most  satisfactory  method  for  obtaining  carbon 
dioxide  is  to  act  upon  calcium  carbonate  in  the  form  of 
marble,  with  a  mixture  of  equal  parts  of  concentrated 
hydrochloric  acid  and  water. 

As  a  constant  supply  of  carbon  dioxide  is  very  advan- 
tageous for  many  experiments,  it  is  advisable  to  prepare 
a  Kipp  generator  (Fig.  17,  p.  46),  filling  the  receptacle  with 
small  fragments  of  marble  and  using  hydrochloric  acid 
diluted  as  above. 


CARBON   DIOXIDE  305 

The  general  use  to  which  cylinders  of  the  liquefied  gas 
(Ex.  29,  p.  307)  have  been  applied  renders  it  easy  to  procure 
them.  They  may  be  advantageously  used  for  obtaining  a 
constant  stream  of  the  gas. 

Owing  to  its  great  specific  gravity,  carbon  dioxide  is 
almost  invariably  collected  by  displacement.  Its  solu- 
bility in  water  renders  it  advisable  to  collect  the  gas 
over  mercury,  in  case  the  displacement  method  cannot 
be  used. 

CaCOg  +  2  HCl  =  CaCla  +  U.O  +  COg. 

Kipp  generator  for  CO2  ;  marble  fragments. 

24.  From  baking-powder.  — A  few  grams  of  baking-powder 
are  heated  in  a  dry  test-tube  and  the  issuing  gas  tested  with 
a  lighted  splinter.  The  presence  of  organic  vapors  inter- 
feres with  this  experiment  somewhat,  and  the  powder  should 
be  but  gently  heated. 

Hydrochloric  acid  added  to  some  baking-powder  in  a 
cylinder  gives  rise  to  an  evolution  of  carbon  dioxide. 

25.  Carbon    dioxide  a  product    of    fermentation.  —  The 

importance  of  fermentation,  with  the  liberation  of  carbon 
dioxide  during  the  process,  makes  it  desirable  to  show  this 
operation  on  the  lecture  table. 

A  mixture  of  50  cc.  of  molasses  and  400  cc.  of  water  with 
about  one-half  of  a  fresh,  compressed  yeast-cake  is  placed 
in  a  500  cc.  flask  fitted  with  a  cork  and  an  elbow.  A  gas 
washing-bottle  containing  lime-water  is  connected  with  the 
elbow,  and  the  whole  apparatus  allowed  to  stand  in  a  warm 
place  till  the  next  exercise.  The  carbon  dioxide  liberated 
will  force  its  way  through  the  lime-water,  rendering  it  turbid. 
An  empty  gas  washing-bottle  may  be  inserted  between  the 
elbow  and  the  bottle  containing  lime-water,  and  the  gas 


306  CHEMICAL   LECTURE   EXPERIMENTS 

in  this  cylinder  may  be  tested  with  a  lighted  candle  at  the 
close  of  the  experiment. 

500  cc.  flask  ;  2  gas  washing-bottles ;  molasses ;  yeast-cake  ;  lime- 
water. 

26.  Carbon  dioxide  in  beverages.  —  (a)  The  presence  of 
carbon  dioxide  in  wine  or  beer  may  be  shown  by  heating  a 

portion  of  the  liquor  in  a  flask  fitted  with  a 

^^Tj  cork  and  a  bent  glass  tube  dipping  into  lime- 

|Qp=^      water.     On  the  application  of  gentle  heat,  the 

Jtk^^^         gas  is  liberated,  and  a  cloudiness  is  produced 

in  the  lime-water. 

(&)  A  glass  siphon  of  "  soda-water "  (Fig. 
122)  is  inverted,  and,  by  pressing  the  valve, 
a  large  quantity  of  carbon  dioxide  is  with- 
drawn. 

Fig  122  ^  little  of  the  liquid  from  a  siphon  is  poured 

into  the  flask  used  above,  and  the  carbon  di- 
oxide, given  off  on  standing  or  more  quickly  by  gentle  heat- 
ing, is  conducted  into  lime-water  as  before. 

Wine  or  beer  ;  siphon  of  "  soda-water"  ;  lime-water. 

27.  Presence  of  carbon  dioxide  in  air.  —  If  a  small  quan- 
tity of  lime-water  or  barium  hydroxide  solution  is  allowed 
to  stand  for  several  hours  in  a  crystallizing  dish  in  the  open 
air,  the  liquid  will  be  covered  with  a  white  film  of  calcium 
or  barium  carbonate. 

The  formation  of  the  carbonate  may  be  more  rapidly 
obtained  by  drawing  a  current  of  air  with  a  filter-pump 
through  a  gas  washing-bottle  containing  either  of  the  above 
solutions.  In  a  few  minutes  a  marked  turbidity  will 
appear  in  the  liquid. 

Filter-pump  ;  gas  washing-bottle  ;  crystallizing  dishes  ;  lime-water  ; 
Ba(0H)2  solution. 


CARBON   DIOXIDE  307 

28.  Carbon  dioxide  in  expired  air.  —  That  expired  air 
contains  carbonic  acid  in  considerable  quantities  is  simply 
shown  by  blowing  through  a  glass  tube  into  50  cc.  of  lime- 
water  in  a  small  beaker.  A  white  precipitate  of  calcium 
carbonate  is  immediately  formed.  Continued  blowing 
through  the  tube  results  in  redissolving  the  calcium  car- 
bonate by  the  excess  of  carbonic  acid,  forming  calcium  acid 
carbonate.  Heating  the  solution  in  a  test-tube  drives  off 
the  carbonic  acid  and  causes  the  precipitate  to  reappear. 

In  case  barium  hydroxide  is  used,  the  precipitate  will  not 
easily  be  redissolved. 

100  cc.  beaker  ;  lime-water  ;  Ba(0H)2  solution. 
PROPERTIES 

29.  Preparation  of  solid  carbon  dioxide.  —  When  liquid 
carbon  dioxide  is  allowed  to  expand  suddenly,  the  tempera- 
ture is  lowered  to  such  an  extent  that  a  portion  of  the  liquid 
solidifies. 

Liquefied  carbon  dioxide  is  an  article  of  commerce  readily 
obtained  at  a  very  low  price,  being  much  used  in  preparing 
aerated  beverages.  It  is  ordinarily  transported  in  steel  cyl- 
inders about  1.5  m.  high  and  20  cm.  in  diameter.  When 
standing  in  an  upright  position  with  the  valve  end  upper- 
most, the  valve  may  be  opened  and  carbon  dioxide  gas  with- 
drawn. If,  however,  the  cylinder  is  inverted  and  the  valve 
opened,  the  liquefied  gas  is  forced  out  at  the  bottom  in  a  fine 
stream,  which  immediately  expands  to  the  gaseous  form, 
producing  a  great  lowering  of  the  temperature.  Numerous 
forms  of  apparatus  have  been  devised  into  which  the  stream 
of  gas  is  allowed  to  expand  with  a  solidification  of  a  portion 
of  the  gas.  A  black  flannel  bag,  some  20  to  30  cm.  square,  is 
an  excellent  substitute  for  apparatus  of  this  kind,  and  when 
securely  fastened  to  the  valve-nozzle  permits  the  collection 


308 


CHEMICAL   LECTURE    EXPERIMENTS 


Fig.  123 


of  considerable  quantities  of  solid  carbon  dioxide.  The  bag 
is  preferably  made  with  a  drawstring  which  may  be  used  to 
fasten  it  securely  to  the  valve-piece 
(Fig.  123). 

As  it  is  not  infrequent  in  charging 
these  cylinders  with  the  liquefied  gas 
that  varying  quantities  Of  water  are 
inadvertently  introduced,  it  is  im- 
portant to  open  the  valve  carefully 
and  draw  off  any  water  before  fasten- 
ing the  bag  to  the  valve-piece.  This 
operation  should  be  carried  out  before 
the  lecture.  As  soon  as  all  the  water 
is  forced  out,  the  gas  will  begin  to 
escape  and  the  nozzle  will  become 
covered  with  frost.  The  bag  is  then 
attached,  and,  by  opening  the  valve, 
a  brisk  stream  of  the  liquefied  gas 
allowed  to  enter  it.  The  finer  particles  of  the  solidified  gas 
will  be  forced  through  the  cloth  and  will  fall  as  a  white  fog 
to  the  floor. 

On  removing  the  bag  a  considerable  quantity  of  the  solid 
carbon  dioxide  will  be  found  as  a  snow-like  mass  which  is 
shaken  into  a  cardboard  box.  If  the  bag  is  turned  inside 
out,  it  will  be  found  to  be  lined  with  the  white  solid.  The 
operation  may  be  repeated,  and  the  solid  obtained  in  any 
quantity. 

In  spite  of  the  very  low  temperature  of  the  solid  it  re- 
mains quite  a  long  time  in  the  air  without  disappearing,  and 
this  property  is  especially  well  shown  if  the  solid  is  pressed 
into  a  cake  or  rod,  which  may  then  be  placed  on  a  piece  of 
felt  on  a  plate  and  passed  around  the  lecture  room.  A  mould 
is  made  by  boring  a  1.5  cm.  hole  in  a  block  of  wood.  A 
paper  tube  is  fitted  to  the  hole,  and  the  end  bent  in  upon 


CARBON  DIOXIDE  309 

itself  to  make  a  bottom  for  the  tube.  It  is  then  filled  with 
the  solid  carbon  dioxide,  which  is  pressed  down  hard  with  a 
pencil  or  rod  of  wood.  When  the  paper  tube  is  filled,  it  is 
withdrawn,  the  paper  unrolled,  and  the  rod  of  solid  carbon 
dioxide  placed  on  a  piece  of  felt  or  cotton-wool. 

The  greatest  care  should  be  exercised  in  handling  the  solid 
not  to  press  it  hard  with  the  fingers ;  for  though  the  rod  may 
be  laid  on  the  hand  with  no  sense  of  discomfort,  the  effect 
of  pressure  is  to  break  the  film  of  gas  between  the  solid 
and  the  warm  hand  and  thus  cause  a  severe  burn.  So  long 
as  no  pressure  is  applied  the  solid  may  be  handled  with 
impunity.  In  general,  a  paper  scoop  or  a  horn  spatula  will 
be  found  most  serviceable  in  handling  the  solid. 

Steel  cylinder  of  liquefied  CO2 ;  valve-wrench  ;  flannel  bag ;  card- 
board box  ;  block  of  wood  with  1,5  cm.  hole  ;  paper  tube  ;  paper  scoop  ; 
horn  spatula  ;  rod  of  wood  or  lead-pencil ;  felt ;  plate. 

30.  Experiments  with  solid  carbon  dioxide. — A  few  pieces 
are  placed  in  a  clean,  dry  cylinder  and  allowed  to  stand  for 
a  few  moments.  Sufiicient  gas  will  be  evolved  from  the 
solid  to  fill  the  cylinder,  and  a  lighted  taper  will  be  extin- 
guished when  thrust  into  the  jar. 

A  piece  of  the  solid  is  placed  in  the  ginger-ale  bottle  of 
Ex.  30,  p.  67,  which  is  then  corked  with  a  rubber  stopper. 
In  a  short  time  the  evolution  of  gas  within  the  bottle  will 
have  generated  enough  pressure  to  blow  the  stopper  out  of 
the  neck. 

A  one-holed  rubber  stopper  carrying  a  delivery-tube  is  in- 
serted in  the  mouth  of  the  bottle  and  the  evolved  gas  caused 
to  bubble  through  lime-water,  where  a  turbidity  will  appear. 

A  portion  of  the  gas  escaping  from  the  delivery-tube  is  also 
collected  in  a  cylinder  over  water  at  the  pneumatic  trough. 

Dry  cylinder ;  ginger-ale  bottle  (Ex.  30,  p.  67)  ;  rubber  stopper  ; 
delivery-tube ;  lime-water. 


L 


310  CHEMICAL   LECTURE   EXPERIMENTS 

31.  Freezing  water  with  solid  carbon  dioxide.  — A  small 
beaker  is  placed  upon  a  few  drops  of  water  on  a  block  of 
wood,  and  fragments  of  solid  carbon  dioxide  are  placed  in 
it.  In  a  very  few  moments  the  water  will  be  frozen,  and  the 
beaker  will  be  cemented  to  the  wood. 

Block  of  wood  ;  small  beaker  ;  solid  CO2. 

32.  Freezing  mercury  with  solid  carbon  dioxide.  —  Inas- 
much as  the  temperature  of  solid  carbon  dioxide  is  —  79°, 
mercury,  when  cooled  with  it,  may  be  frozen  to  a  hard  solid. 

(a)  A  few  cubic  centimeters  of  dry  mercury  are  placed  in  an 
evaporating-dish,  which  is  in  turn  placed  on  a  wad  of  cotton- 
wool, and  a  centimeter  layer  of  solid  carbon  dioxide  is  placed 
upon  it.  A  wad  of  cotton-wool  or  a  piece  of  cardboard  should 
be  placed  over  it  and  the  dish  allowed  to  stand  for  several 
minutes.  On  inverting  the  dish  the  mercury  will  be  found 
to  be  a  solid,  which  may,  at  times,  adhere  to  the  dish.  By 
gentle  tapping  it  may  be  dislodged,  or  a  piece  of  paper  may 
previously  be  placed  in  the  dish  between  the  mercury  and 
the  porcelain.  The  evaporating-dish  should  be  inverted  and 
the  frozen  mercury  manipulated  over  a  larger  dish  to  catch 
any  drops  of  the  mercury  as  it  melts.  An  iron  wire  may 
advantageously  be  frozen  into  the  mercury  to  facilitate  in 
lifting  the  solid. 

(b)  A  much  more  striking  method  of  showing  the  solidi- 
fication of  mercury  consists  of  freezing  the  metal  in  the 
form  of  a  ring,  which  is  subsequently  suspended  and  lowered 
into  a  jar  of  cold  water.  For  this  purpose  a  mould  consist- 
ing of  a  block  of  wood  in  which  a  circular  groove  has  been 
cut  approximately  1  cm.  deep  and  1  cm.  wide,  the  internal 
diameter  of  which  is  about  7  cm.,  is  necessary  (Fig.  124). 
The  circular  space  is  filled  with  a  7  mm.  layer  of  mercury, 
and,  after  placing  the  mould  on  a  large  porcelain  dish,  the 
mercury  is  covered  with  a  centimeter  layer  of  solid  carbon 


CARBON   DIOXIDE 


311 


dioxide.  It  is  advisable  to  iill  in  the  spaces  around  the 
block  of  wood  with  cotton-wool  and  to  cover  the  dish  with 
a  piece  of  cardboard.  Af- 
ter -several  minutes  the 
mercury  will  be  frozen 
solid,  and  by  inverting 
the  mould  the  ring  will 
fall  out.  The  mercury  is 
then  quickly  raised  with 
the  horn  spatula,  placed 
upon  a  glass  hook,  and 
lowered  into  a  large  ves- 
sel of  water  which  is  near 
the  freezing  point.  In- 
stantly the  mercury  ring  becomes  covered  with  an  ice  ring, 
then  melts,  and  the  mercury  falls  to  the  bottom  of  the  vessel. 
The  ice  ring  remains  on  the  glass  hook  for  several  moments 
before  melting. 

While  the  addition  of  anhydrous  ether  lowers  the  temper- 
ature of  the  solid  carbon  dioxide  somewhat,  the  mercury  can 
be  frozen  without  the  addition  of  ether,  provided  sufficient 
time  is  allowed  to  complete  the  solidification. 

Cotton-wool ;  evaporating-dish  ;  large  porcelain  dish  ;  wooden  mould; 
horn  spatula ;  glass  hook ;  large  vessel  of  ice-cold  water ;  dry  Hg ; 
Fe  wire  ;  solid  CO2. 


33.  Specific  gravity.  —  Carbon  dioxide  is  much  heavier 
than  air,  and  is  the  subject  of  many  experiments  illustrating 
this  property. 

A  liter  beaker  is  supported  on  the  arm  of  the  lecture- 
balance  and  the  system  brought  into  equilibrium.  If  a  cur- 
rent of  carbon  dioxide  is  allowed  to  flow  from  a  tube  held 
above  the  beaker,  it  will  collect  in  the  bottom,  expelling  the 
air  and  causing  a  marked  increase  in  weight. 


312  CHEMICAL   LECTURE   EXPERIMENTS 

Instead  of  conducting  the  carbon  dioxide  into  the  beaker 
in  a  stream,  a  large  cylinder  may  be  filled  with  the  gas, 
which  may  then  be  poured  rapidly  into  the  suspended 
beaker.  A  marked  inclination  of  the  pointer  on  the 
balance  is  immediately  observed. 

.    Lecture-balance  ;  2  1.  beakers  ;  CO2  generator. 

34.  Quantitative  estimation  of  the  specific  gravity  of 
carbon  dioxide.  —  It  is  possible  to  determine  with  consider- 
able accuracy  the  specific  gravity  of  carbon  dioxide  in  a 
manner  analogous  to  that  described  for  determining  the 
specific  gravity  of  hydrogen  (Ex.  10,  p.  48). 

A  narrow-necked,  graduated  liter  flask  is  suspended  on 
one  arm  of  the  lecture-balance  with  the  mouth  uppermost. 
The  system  is  then  brought  into  equilibrium.  A  current  of 
dry  carbon  dioxide  is  conducted  through  a  long  glass  tube 
inserted  in  the  neck  of  the  flask  and  extending  to  the 
bottom.  In  a  few  minutes  the  air  will  have  been  entirely 
driven  out,  and  by  slowly  withdrawing  the  tube  the  flask  is 
completely  filled  with  carbon  dioxide.  As  the  air  originally 
in  the  flask  has  been  replaced  by  a  heavier  gas,  it  will  be 
necessary  to  add  more  weights  to  the  other  pan  of  the  bal° 
ance  to  restore  the  equilibrium.  With  a  normal  barometric 
pressure  and  a  temperature  of  15°,  0.63  g.  will  have  to 
be  added.  A  liter  of  air  under  these  conditions  of  tempera- 
ture and  pressure  weighs  1.225  g.,  hence  a  liter  of  carbon 
dioxide  weighs  1.225  plus  0.63,  which  equals  1.855  g.  Com- 
pared to  the  weight  of  a  similar  volume  of  air  it  is  readily 
calculated  that  the  specific  gravity  of  carbon  dioxide  is 
1.51. 

If  the  barometric  and  thermometric  conditions  vary 
widely  from  those  given  above,  it  will  be  necessary,  if  the 
greatest  accuracy  is  desired,  to  apply  the  usual  corrections 


CARBON   DIOXIDE 


313 


to  determine  the  weight  of  a  liter  of  air  under  the  observed 
conditions. 

Lecture-balance  ;  liter  graduated  flask ;  weights ;  H2SO4  gas  wash- 
ing-bottle ;  CO2  generator. 

35.  Soap-bubbles  float  on  carbon  dioxide.  —  If  a  soap- 
bubble  is  allowed  to  fall  into  a  large  jar  which  is  half  full 
of  carbon  dioxide,  it  will  settle  in  the  jar  to  the  level  of  the 
carbon  dioxide  and  then  float  on  top  of  this  gas. 

A  tall,  wide-mouthed  jar,  such  as  is  used  for  large  speci- 
mens in  museums,  is  half  filled  with  carbon  dioxide.  A 
small  soap-bubble,  blown  on  the  end  of  a  thistle-tube,  is 
allowed  to  fall  into  the  jar,  where  it  will  float  on  the  sur- 
face of  the  carbon  dioxide. 

Thistle-tube  ;  large  jar  (8  or  10  1.)  half  filled  with  CO2  ;  soap  sol. 


36.  Carbon  dioxide  rotates  a  paper  wheel.  —  The  great 
specific  gravity  of  carbon  dioxide  may  also  be  shown  by 
pouring  a  liter  of  the  gas  upon  a  cardboard  wheel  having 
paper  cups  on  its  periphery.  As  the 
carbon  dioxide  collects  in  the  cups 
the  wheel  is  caused  to  rotate  on  its 
axis. 

A  piece  of  stout  cardboard  is  cut 
into  a  circle  20  cm.  in  diameter,  ten  or 
twelve  small  paper  cups  are  pasted 
on  the  rim,  and  a  long  needle  is  thrust 
through  the  centre  of  the  wheel  (Fig. 
125).  Two  stout  copper  wires  fast- 
ened to  a  block  of  wood  may  be  so 
bent  as  to  form  the  bearings  on  which  the  needle  is  set.  In 
balancing  the  wheel  it  will  probably  be  necessary  to  add  a 
bit  of  wax  at  different  points  before  securing  perfect  equi- 


Fia.  125 


314  CHEMICAL   LECTURE  EXPERIMENTS 

librium.     When  once  arranged,  the  wheel  will  rotate  quite 
rapidly  if  a  liter  of  carbon  dioxide  is  poured  into  the  cups. 
Cardboard  wheel ;  liter  cylinder  of  CO2. 

37.  Carbon  dioxide  may  be  siphoned.  —  By  reason  of  its 
great  specific  gravity,  carbon  dioxide  may  be  siphoned  from 
one  vessel  to  another. 

A  2  1.  cylinder  is  filled  with  carbon  dioxide  and  its  pres- 
ence established  by  lowering  a  lighted  candle  into  it.  An 
empty  cylinder  of  the  same  size  is  likewise  tested  with  the 
candle  and  the  absence  of  carbon  dioxide  shown.  A  glass 
tube,  with  an  internal  diameter  of  not  less  than  7  mm.,  bent 
in  the  form  of  a  siphon,  is  inserted  in  the  jar  of  carbon 
dioxide,  which  should  be  placed  on  a  box  or  other  support 
above  the  table.  The  siphon  is  started  by  gentle  suction 
with  the  mouth  on  the  longer  arm,  and,  when  the  gas  has 
filled  the  tube,  the  lower  end  is  thrust  into  the  empty  cylin- 
der. However,  as  the  upper  cylinder  is  fixed,  it  is  better 
to  arrange  to  have  the  lower  cylinder  brought  up  from 
beneath.  The  presence  of  the  gas  in  the  longer  arm  of  the 
siphon  will  be  known  by  the  taste.  After  a  few  minutes 
the  gas  will  all  have  left  the  upper  cylinder,  and  a  candle 
will  continue  to  burn  when  lowered  into  it,  while  if  a 
lighted  candle  is  inserted  in  the  lower  cylinder,  it  will  be 
extinguished. 

Two  2  1.  cylinders  ;  siphon  ;  CO2  supply  ;  candle  on  wire. 

38.  Carbon  dioxide  extinguishes  the  flame  of  a  candle.  — 

That  carbon  dioxide  is  heavier  than  air  and  is  a  non-sup- 
porter of  combustion  is  interestingly  shown  by  pouring  2  1. 
of  the  gas  down  into  a  wooden  or  metal  trough  in  which 
five  small  candles  are  burning.  As  the  carbon  dioxide  flows 
down  the  trough,  the  candles  are  extinguished  in  rapid 
succession. 


CARBON   DIOXIDE 


315 


The  trough  may  be  made  by  bending  a  piece  of  tin  1  m. 
long  or  by  tacking  two  pieces  of  wood  together  at  right 
angles.  The  trough  should  be  in- 
clined at  an  angle  of  45°,  and  the 
candles  so  attached  as  to  burn  in 
an  upright  position.  To  prevent 
an  upward  current  of  air,  it  is 
best  to  cut  off  the  lower  part  of  the 
trough  by  means  of  a  block  of 
wood  or  a  piece  of  cardboard  (Fig. 
126).  The  candles  should  be  of 
the  smallest  size  and  are  placed  approximately  15  cm. 
apart. 

Trough  (Fig.  126);  small  candles ;  2  1.  beaker  of  CO2. 


Fig.  126 


39.  Carbon  dioxide  in  expired  air  extinguishes  a  candle 
flame.  —  Air  from  the  lungs  is  collected  in  a  cylinder  over 
water.  By  taking  the  last  portion  of  one  exhalation,  that  is, 
that  which  has  had  the  longer  sojourn  in  the  lungs,  a  gas 
quite  rich  in  carbonic  acid  is  obtained,  and,  indeed,  the 
per  cent  of  this  gas  will  be  so  great  as  to  cause  the  flame  of 
a  candle,  when  it  is  lowered  into  the  cylinder,  to  be  extin- 
guished. By  using  a  flexible  rubber  tube,  which  can  be 
pushed  clear  up  the  inner  wall  of  the  cylinder,  the  gas  may 
be  drawn  back  into  the  lungs  to  become  still  richer  in  car- 
bonic acid.  In  this  case  the  rubber  tube  should  have  its 
end  out  of  water  inside  the  cylinder  when  the  air  is  with- 
drawn, to  prevent  water  from  being  sucked  back  into  the 
mouth.  After  removing  the  cylinder  from  the  pneumatic 
trough  by  covering  it  with  a  glass  plate,  the  lighted  candle 
is  immediately  introduced. 

300  cc.  cylinder ;  pneumatic  trough ;  candle  on  wire  ;  long  clean 
rubber  tube  ;  glass  plate. 


316 


CHEMICAL   LECTUKE   EXPERIMENTS 


40.  Preparation  of  a  supersaturated  solution  of  carbon 
dioxide  (soda  water) .  —  The  technical  preparation  of  a  satu- 
rated aqueous  solution  of  carbon  dioxide  may  be  admirably 
illustrated  on  the  lecture  table  by  means  of  a  patent  device  ^ 
in  which  small  steel  capsules  containing  the  liquefied  gas 
are  used. 

The  apparatus  consists  of  a  wire  or  wicker-covered,  stout- 
walled  bottle  and  a  special  screw-top.  As  explicit  direc- 
tions are  given  with  each  apparatus,  it  need 
only  be  stated  here  that  the  bottle  is  seven- 
eighths  filled  with  cold  distilled  water,  the  top 
screwed  on  carefully,  the  steel  capsule  inserted 
in  the  upper  portion  of  the  metallic  top,  and  the 
gas  liberated  by  screwing  down  a  small  screw- 
cap  (Fig.  127).  The  gas  is  forcibly  driven  in 
a  fine  jet  into  the  water  which,  after  unscrewing 
the  top,  will  be  found  to  be  supercharged  with 
carbon  dioxide.  On  pouring  some  of  the  water 
into  a  beaker  the  excess  of  gas  will  ascend  in 
fine  bubbles. 

The  capsules  are  especially  interesting,  and  the 
difference  in  weight  when  filled  and  when  empty 
is  very  marked.  The  gas  may  be  withdrawn  from  the 
capsule  and  collected  over  water  by  attaching  a  rubber  tube 
to  the  end  of  the  jet  and  very  carefully  screwing  down  the 
small  cap,  a  slow  liberation  of  the  gas  resulting.  The  gas 
issuing  from  the  other  end  of  the  rubber  tube  may  be  col- 
lected in  a  liter  cylinder  over  water. 

The  intense  cold  produced  by  the  evaporation  of  the 
liquid  may  be  shown  by  discharging  a  capsule  in  the  air, 

1  The  apparatus  is  distributed,  by  the  Compressed  Gas  Capsule 
Company  of  New  York,  and  may  be  obtained  in  nearly  every  city  in 
the  United  States.  The  small  steel  capsules  are  sold  under  the  trade 
name  "Sparklets." 


PiQ.  127 


CAEBON   BISULPHIDE  317 

pointing  the  nozzle  down.  As  the  liquid  escapes,  it  forms 
for  a  moment  a  thin  fog  and  the  end  of  the  jet  becomes 
extremely  cold. 

Sparklet  apparatus  (Fig.  127) ;  liter  cylinder ;  rubber  tube ;  pneu- 
matic trough. 

CARBON   BISULPHIDE 

PROPERTIES 

41.  Solvent  action  on  fats.  —  Carbon  disulphide  dissolves 
fats  readily.  A  small  lump  of  tallow  in  a  test-tube  is  cov- 
ered with  carbon  disulphide,  in  which  it  readily  dissolves. 

A  piece  of  paper,  a  portion  of  which  has  been  greased,  is 
dipped  into  carbon  disulphide  and  allowed  to  remain  three 
minutes.  On  withdrawing  the  paper  and  allowing  the  car- 
bon disulphide  to  evaporate,  the  grease  spot  will  have  dis- 
appeared. 

Tallow  ;  greased  paper ;  CS2. 

42.  Production  of  cold  by  the  rapid  evaporation  of  carbon 
disulphide.  —  Fifteen  cubic  centimeters  of  carbon  disulphide 
are  placed  in  a  small  flask  and  covered  with  5  cc.  of  water. 
A  strong  blast  of  air  is  passed  through  the  mixture,  care 
being  taken  to  provide  for  the  removal  of  the  vapors  of  car- 
bon disulphide  to  a  flue  or  hood.  In  a  few  moments  the 
water  in  the  flask  will  be  frozen. 

If  a  current  of  air  is  passed  through  carbon  disulphide  in 
which  a  thermometer  is  placed,  the  temperature  will  rapidly 
fall  to  15°  below  zero. 

Small  wide-mouthed  flask  ;  air-blast ;  thermometer  ;  CS2. 

43.  Comparative  inflammability  of  ether  and  carbon  disul- 
phide. —  A  glass  rod  which  has  been  heated  at  one  end  is 
dipped  into  ether,  which  is  not  ignited  by  it,  and  then  into 
an  evaporating-dish   containing  carbon  disulphide.      Suffi- 


L 


318  CHEMICAL   LECTURE   EXPERIMENTS 

cient  heat  will  have  been  retained  to  ignite  the  carbon  disul- 
phide.  The  ether  and  the  carbon  disulphide  are  both  placed 
in  evaporating-dishes  which  stand  about  30  cm.  apart. 

Two  evaporating-dislies  ;  CSa  ;  ether, 

44.  Combustion  in  oxygen.  —  One  cubic  centimeter  of 
carbon  disulphide  is  placed  in  a  deflagrating-spoon  and  after 
ignition  lowered  into  a  liter  cylinder  of  oxygen.  The  com- 
bustion proceeds  with  great  brilliancy.  If  the  spoon  is 
shaken  somewhat  so  as  to  swash  the  liquid  upon  the  hot 
sides  of  the  spoon,  it  will  evaporate  more  rapidly,  and  con- 
sequently a  larger  flame  will  be  obtained. 

Deflagrating-spoon  ;  liter  cylinder  of  0  ;  CS2. 

45.  Explosion  of  a  mixture  of  carbon  disulphide  vapor 
and  oxygen.  —  A  mixture  of  carbon  disulphide  vapor  and 
oxygen  explodes  vigorously,  though  by  selecting  a  stout- 
walled  cylinder  the  experiment  may  be  safely  performed. 

A  strong  200  cc.  cylinder  is  filled  with  oxygen  into  which 
2  cc.  of  carbon  disulphide  are  poured.  The  cylinder  is  cov- 
ered with  a  cardboard  having  a  hole  in  the  centre,  and  is 
then  vigorously  shaken.  On  applying  a  match  to  the  open- 
ing a  sharp  explosion  is  obtained.  If  a  heavy-walled 
cylinder  is  not  at  hand,  it  is  advisable  to  wrap  the  apparatus 
with  a  towel  to  prevent  damage  from  the  explosion. 

Stout-walled  cylinder  ;  O  supply  ;  CS2. 

46.  Combustion  of  potassium.  —  Potassium  burns  in  the 
vapor  of  carbon  disulphide,  forming  polysulphides  of 
potassium. 

Carbon  disulphide  in  a  100  cc.  flask  is  heated  in  a  beaker 
of  hot  water,  and  the  vapor  conducted  through  a  glass  elbow 
into  a  bulb-tube  containing  a  piece  of  potassium.  Eubber 
must  be  avoided  in  making  any  of  the  connections.     As  soon 


METHANE    (MARSH   GAS) 


319 


as  the  tube  is  filled  with  the  vapor  of  the  disulphide,  the 
potassium  is  heated.     The  metal  burns  vigorously. 

100  cc.  flask  ;  bulb-tube  ;  beaker  of  hot  water ;  CS2  ;  K. 

47.  Combustion  of  iron. — Fine  iron  wire,  when  thrust 
into  the  flame  of  burning  carbon  disulphide,  burns  strongly, 
forming  ferrous  sulphide. 

The  vapor  of  carbon  disulphide  issuing  from  the  glass 
elbow  in  the  flask  of  the  preceding  experiment  is  ignited 
and  the  size  of  the  flame  regulated  by  the  temperature  of 
the  water  in  the  beaker.  Iron  wires  which  have  been 
twisted  together  are  inserted  in  the  flame.  The  molten 
globules  of  iron  sulphide  formed  may  be  tested  with  hydro- 
chloric acid,  and  the  evolution  of  hydrogen  sulphide  shown. 

100  cc.  flask  ;  beaker  of  hot  water ;  cork  and  elbow  ;  CS2 ;  bundle 
of  fine  iron  wires. 


METHANE    (MARSH   GAS) 

48.  Preparation  from  sodium  acetate.  —  Sodium  acetate, 
when  heated  in  the  presence  of  soda-lime,  decomposes,  lib- 
erating methane  or  marsh  gas. 

Fifteen  grams  of  fused  so- 
dium acetate  are  pulverized 
and  mixed  with  an  equal 
weight  of  fused  soda-lime. 
The  mixture  is  placed  in  a 
100  cc.  Jena  glass  Erlenmeyer 
flask  fitted  with  a  one-holed 
cork  and  a  wide  delivery-tube 
(Fig.  128).  The  flask  is  grad- 
ually heated  and,  after  all  air 

has  been  driven  out,  the  gas  is  collected  in  several  cylinders 
for  use  in  the  following  experiments.     The  importance  of 


Fig.  128 


320  CHEMICAL   LECTURE   EXPERIMENTS 

having  water-free  materials  cannot  be  too  strongly  empha- 
sized, as  condensed  water  is  likely  to  break  the  flask. 

100  cc.  Jena  glass  Erlenmeyer  flask ;  pneumatic  trough ;  several 
cylinders  ;  fused  sodium  acetate  ;  fused  soda- lime. 

49.  Marsh  gas  a  non-supporter  of  combustion.  —  A  burn- 
ing candle  thrust  into  an  inverted  cylinder  of  marsh  gas  is 
immediately  extinguished. 

Candle  on  wire  ;  liter  cylinder  of  CH4. 

50.  Explosion  with  oxygen.  —  Two  volumes  of  oxygen 
and  1  volume  of  marsh  gas  are  introduced  into  a  thick- 
walled  100  cc.  cylinder  having  a  cardboard  cover  with  a 
5  mm.  hole  in  the  centre.  On  igniting  the  mixture,  a  strong 
explosion  will  be  obtained.  A  thick-walled  cylinder  or  a 
round-bottomed  ginger-ale  bottle  should  be  used  for  this 
experiment,  and  as  a  special  safeguard  the  vessel  should  be 
wrapped  with  a  towel. 

100  cc.  stout- walled  cylinder  filled  |  with  CH4  and  |  with  0. 

ETHYLENE 

51.  Preparation  from  alcohol  and  snlphnric  acid.  —  Sul- 
phuric acid  extracts  water  from  ethyl  alcohol,  liberating 
ethylene. 

One  hundred  and  twenty  cubic  centimeters  of  concentrated 
sulphuric  acid  are  cautiously  poured,  with  constant  stirring, 
into  30  cc.  of  ethyl  a*lcohol.  After  cooling,  the  mixture  is 
poured  into  a  liter  flask  one-fourth  filled  with  coarse  sand. 
The  flask  is  fitted  with  a  cork,  a  safety-tubej  and  a  wide 
delivery-tube  (Fig.  129).  On  gently  heating  the  mixture  a 
rapid  evolution  of  ethylene  is  obtained,  which  may  be  col- 
lected in  a  large  tubulated  bell-jar  for  Ex.  53,  and  in  several 


ETHYLENE 


321 


small  cylinders  for  other  experiments.  As  the  mixture  is 
liable  to  char  and  froth  badly,  the  heat  should  be  very  care- 
fully applied.  The  gas  ob- 
tained in  this  reaction  is  not 
perfectly  pure,  and  should 
be  washed  by  conducting  it 
through  a  solution  of  sodium 
hydroxide,  if  the  pure  gas  is 
desired.      Owing  to  its  solu- 

cold    water,    it    is 

to   have  the  water 

pneumatic      trough 


bility    in 
advisable 
in      the 
warm. 

C2HeO=C2H4  +  H20. 


^r- —         ^ 


Fig.  129 


Liter  flask ;  gas  washing-bottle ;  tubulated  bell-jar ;  pneumatic 
trough  with  warm  water  ;  cylinders ;  sand  ;  ethyl  alcohol. 

52.  Preparation  from  ethylene  dibromide.  —  One  cubic 
centimeter  of  alcohol  and  2  cc.  of  ethylene  dibromide  are 
warmed  with  a  few  pieces  of  granulated  zinc  in  a  test-tube. 
The  zinc  combines  with  the  bromine,  setting  free  ethylene, 
which  may  be  ignited  at  the  mouth  of  the  tube. 

CaH^Bra  +  Zn  =  ZnBrg  +  C2H4. 

Alcohol ;  ethylene  dibromide ;  granulated  Zn. 

53.  Decomposition  by  heat.  —  Ethylene  is  decomposed  at 
a  high  temperature  with  the  liberation  of  carbon. 

The  gas  from  a  gas-holder,  or  from  the  bell-jar,  Ex.  51,  is 
conducted  through  a  bulb-tube.  After  all  air  has  been  driven 
out  of  the  apparatus,  the  bulb- tube  is  strongly  heated  in  a 
blast. lamp.  By  rotating  the  bulb,  a  thin  mirror-like  deposit 
of  carbon  may  be  obtained  all  over  the  interior  of  the  bulb. 

Bulb-tube  ;  blast-lamp;  C2H4  supply. 

Y 


322  CHEMICAL   LECTURE   EXPERIMENTS 

54.  Absorption  by  cold  water.  —  The  absorption  of  ethy- 
lene in  cold  water  may  be  shown  by  a  series  of  experiments 
similar  to  those  used  to  illustrate  the  solubility  of  hydrogen 
sulphide  in  water  (Ex.  17,  p.  140). 

55.  Union  with  bromine.  —  Ethylene  and  bromine  unite 
directly,  forming  ethylene  dibromide. 

A  2  1.  flask  is  filled  with  ethylene,  and  2  cc.  of  bromine 
are  added.  The  bromine  fumes  are  all  absorbed,  and,  after 
a  thorough  shaking,  a  colorless  oil,  ethylene  dibromide, 
remains  on  the  bottom  of  the  flask.  If  an  excess  of  bromine 
is  used,  the  oil  will  be  colored,  and  it  will  be  necessary  to 
wash  it  with  a  little  sodium  hydroxide  solution  to  remove 
the  free  bromine.  The  oil,  which  possesses  an  ethereal  odor, 
may  be  poured  into  a  cylinder  containing  water.  The  oil 
is  heavier  than  water. 

C2H4  +  Bra  =  CaH^Brg. 

2  1.  flask  filled  with  C2H4  ;  cylinder  ;  Br. 

56.  Absorption  by  bromine.  —  The  absorption  of  ethylene 
by  bromine  is  markedly  shown  by  collecting  100  cc.  of  the 
gas  in  the  eudiometer  (Eig.  11,  p.  26),  and  allowing  one  cubic 
centimeter  of  bromine  to  trickle  very  slowly  down  the  inside 
of  the  tube.  The  bromine  in  the  bulb  should  be  covered 
with  water  to  prevent  the  escape  of  bromine  fumes.  As 
the  bromine  comes  in  contact  with  the  gas,  its  color  is  imme- 
diately discharged,  the  volume  of  the  gas  rapidly  diminishes, 
and  the  oily  dibromide  formed  drops  to  the  bottom  of  the 
vessel. 

Eudiometer  (Fig.  11,  p.  26)  ;  C2H4  supply ;  Br. 

57.  Action  of  chlorine  on  ethylene.  —  Chlorine  and  ethy- 
lene unite  to  form  ethylene  dichloride,  an  oily  liquid. 

Two  hundred  cubic  centimeters  of  ethylene  are  introduced 


ACETYLENE  823 

at  the  pneumatic  trough  into  a  500  cc.  cylinder  filled  with 
water,  and  chlorine  is  then  admitted,  a  few  bubbles  at  a  time. 
It  will  unite  with  the  ethylene,  forming  oily  drops  of  the 
dichloride,  which  float  as  a  film  on  the  surface  of  the  water, 
and  finally  settle  to  the  bottom  of  the  trough.  The  volume 
of  the  gas  is  diminished. 

C2XI4  "h  d2  =  C2-H.4d2« 

500  cc.  cylinder  ;  C2H4  ;  CI  supply. 

ACETYLENE 

58.  Preparation  from  ethylene  dibromide  and  alcoholic 
potash.  —  Potassium  hydroxide,  in  alcoholic  solution,  ab- 
stracts hydrobromic  acid  from  ethylene  dibromide,  with  the 
formation  of  acetylene. 

Alcoholic  potash  is  made  by  adding  a  stick  of  caustic 
potash  to  10  or  15  cc.  of  alcohol,  and  pouring  off  the  solution 
when  saturated. 

If  3  or  4  cc.  of  alcoholic  potash  in  a  test-tube  are  heated 
just  to  boiling,  and  a  few  drops  of  ethylene  dibromide  added, 
a  gas  is  given  off,  which,  on  ignition,  is  readily  recognized 
as  acetylene. 

CgH^Brs  +  2  KOH  =  2  KBr  +  2  H2O  -f-  C2H2. 

Alcohol ;  potassium  hydroxide  (stick)  ;  ethylene  dibromide. 

59.  Preparation  from  calcium  carbide.  —  (a)  A  few  pieces 
of  calcium  carbide  in  a  dry  test-tube  are  treated  with  a  few 
drops  of  water.  The  evolution  of  gas  is  very  rapid,  and  on 
ignition,  the  characteristic  luminous,  sooty  flame  of  acetylene 
is  readily  recognized. 

CaCg  -i-  H2O  =  CaO  -f-  C2H2. 
CaO  +  H2O  =  Ca(0H)2. 
Calcium  carbide  in  small  pieces. 


324       CHEMICAL  LECTURE  EXPERIMENTS 

(6)  A  more  striking  decomposition  of  calcium  carbide  by 
water  is  obtained  when  a  5  cm.  piece  is  placed  on  a  plate, 
and  a  fine  jet  of  water  from  a  wash-bottle  or  tap  is  directed 
on  it.  The  escaping  gas  can  be  ignited,  and  the  flame 
increases  as  more  water  is  added. 

Calcium  carbide  is  now  obtainable  in  the  market  in  tin 
cans  for  use  with  bicycle  lamps.  It  should  be  preserved  in 
tightly  sealed  bottles,  as  it  absorbs  moisture  from  the  air, 
and  thereby  is  decomposed. 

Wash-bottle  ;  plate  ;  CaC2. 

60.  Formation  by  the  incomplete  combustion  of  illumi- 
nating gas.  —  In  the  incomplete  combustion  of  illuminating 
gas  (Ex.  6,  p.  345)  small  quantities  of  acetylene  are  formed. 
This  phenomenon  is  also  observed  when  a  Bunsen  burner 
"  strikes  back." 

A  Bunsen  burner,  burning  at  the  base,  is  placed  under 
the  inverted  thistle-tube  in  the  apparatus  (Fig.  31,  p.  62). 
A  sufficient  quantity  of  ammoniacal  cuprous  chloride  solu- 
tion is  placed  in  the  U-tube  to  cover  the  bend.  A  gentle 
suction  is  maintained  through  the  apparatus  and  in  a  few 
moments  a  precipitate  of  red  cuprous  acetylide  is  formed. 

Apparatus  (Fig.  31,  p.  62)  ;  ammoniacal  cuprous  chloride  solution. 

ILLUMINATING   GAS    (COAL   GAS) 

61.  Preparation.  —  Coal  or  wood,  when  subjected  to  dry 
distillation,  yields  considerable  quantities  of  a  gaseous  mix- 
ture consisting  chiefly  of  hydrogen  and  methane,  together 
with  some  of  the  higher  hydrocarbons. 

A  few  grams  of  pulverized  anthracite  coal  are  strongly 
heated  in  a  hard-glass  test-tube.  The  gas  evolved  may  be 
ignited  at  the  mouth  of  the  tube,  where  it  burns  with  a 
feebly  luminous  flame. 


ILLUMINATING   GAS    (COAL   GAS) 


325 


Bituminous  coal,  when  heated  in  a  test-tube,  yields  large 
quantities  of  a  gas  which  burns  at  the  mouth  of  the  tube 
with  a  luminous,  smoky  flame. 

Bits  of  wood  heated  in  a  test-tube  yield  a  gas  which  burns 
with  a  luminous  flame. 


Hard-glass  test-tubes 
wood. 


anthracite  and  bituminous  coal ;  chips  of 


62.   Preparation  by  the  distillation  of  bituminous  coal.  — 

A  500  cc.  Jena  glass  retort  is  one-third  filled  with  pulverized 

bituminous  coal,  and  the  neck 

is  thrust   into  a  filter-bottle 

whose  side  tube  is  provided 

with  a  glass  jet  (Fig.  130). 

The     retort     is     cautiously 

heated,  and  the  gas  evolved 

is   allowed   to   drive  out  all 

air  before  it  is  ignited  at  the 

jet.      The  gas  burns  with  a 

luminous   flame.      A  certain 

amount   of    tarry   matter   is 

distilled  over  and  condenses 

with  some  water  in  the  filter-flask,  which  should  be  kept 

cold  by  immersion  in  water. 


Fig.  130 


Apparatus    (Fig.  130);   500   cc.   retort 
glass  jet ;  pulverized  bituminous  coal. 


sand-bath ;   filter-bottle ; 


63.  Soap-bubbles  filled  with  illuminating  gas  rise  in 
the  air.  —  Soap-bubbles  may  be  blown  with  illuminating 
gas,  as  described  in  Ex.  13,  p.  52.  As  they  ascend,  the 
bubbles  may  be  ignited  by  touching  them  with  a  burning 
taper  on  the  end  of  a  long  stick. 


Thistle-tube  ;  candle  on  long  stick ;  soap  solution. 


326 


CHEMICAL  LECTURE  EXPERIMENTS 


64.    Explosion  of  a  mixture  of  illuminating  gas  and  air. 

(a)  The  explosion  of  a  mixture  of  air  and  illuminating 
gas  is  best  shown  by  means  of  the  fol- 
A  lowing  apparatus.     The  middle  neck 

of  a  liter  three-necked  Wolff  bottle 
(Fig.  131)  is  provided  with  a  cork  and 
a  20  cm.  length  of  combustion  tubing, 
1  cm.  internal  diameter.  Coal  gas  is 
conducted  through  a  glass  tube  in  one 
of  the  necks,  and  the  third  is  closed 
with  a  solid  cork.  All  the  necks 
should  preferably  be  as  wide  as  pos- 
sible. Illuminating  gas  is  conducted 
through  the  glass  tube,  extending  to 
the  bottom  of  the  bottle  until  all  air 
is  expelled,  and  the  gas  is  then  ignited 
as  it  issues  from  the  large  glass  tube 
in  the  middle  neck.  On  cutting  off 
Fig.  131  the   gas  and  simultaneously  removing 

the  cork  in  the  third  neck,  the  flame 
increases  in  size,  though  diminishing  in  intensity,  and  as 
soon  as  enough  air  has  been  drawn  through  the  open  neck 
to  produce  an  explosive  mixture  in  the  bottle,  the  flame 
strikes  back  through  the  tube,  producing  a  loud,  though 
harmless,  explosion. 


Apparatus  (Fig.  131);  1  liter  S-necked  Wolff  bottle 
tubing. 


combustion 


(6)  The  tubulated  bell-jar,  with  cork  and  glass  tube  used 
in  Ex.  29,  p.  67,  may  also  be  used  to  produce  an  explosion 
of  illuminating  gas  and  air. 


65.    Combustion  on  platinized  asbestos.  —  Platinized  as- 
bestos (Ex.  24,  p.  61)  is  heated  to  incandescence  in  a  Bunsen 


ILLUMINATING   GAS    (COAL   GAS)  327 

burner.  On  turning  out  the  gas  the  asbestos  ceases  to  be 
luminous.  If  the  gas  is  now  turned  on,  the  asbestos  will 
immediately  glow,  but  the  gas  is  re-ignited  with  difficulty. 
If  the  air-holes  at  the  base  of  the  burner  are  closed  so  that 
no  air  can  enter,  the  asbestos  will  again  cease  to  glow, 
as  there  is  no  air  in  the  middle  of  the  gas-jet  to  cause 
combustion.  On  opening  the  air-holes,  the  asbestos  again 
becomes  luminous,  owing  to  the  presence  of  the  mixture  of 
gas  and  air. 

Pt  asbestos  (Ex.  24,  p.  61). 


THE   NATUEE    OF   FLAME 


STRUCTURE   OF   FLAME 

1.  The  Bunsen  burner.  —  A  burner  having  an  air-regu- 
lating device  for  closing  the  air-holes  at  the  base  of  the 
burner-tube  should  be  used  in  the  following  experiments. 

The  air-holes  should  be 
closed,  and  then  the 
burner  lighted.  The 
large,  luminous,  flicker- 
ing flame  should  be 
compared  with  the 
flame  obtained  by  un- 
screwing the  burner- 
tube  and  lighting  the 
gas  as  it  issues  from 
the  fine  jet  (Fig.  132). 
The  ratio  of  the  cross- 
sections  of  the  tubes 
through  which  the  gas 
is  issuing  in  both  cases 
should  be  noted. 
After  replacing  the  burner-tube,  the  air-holes  still  being 
closed,  the  burner  should  again  be  lighted  and  the  air-holes 
gradually  opened.  The  variations  in  the  nature  of  the  flame 
from  the  flickering,  luminous  flame  to  the  steady,  non-lumi- 
nous flame  should  be  noticed. 

328 


Fig.  132 


STRUCTURE   OP   FLAME 


329 


That  a  certain  ratio  must  exist  between  the  proportion  of 
gas  and  air  mixing  in  the  burner-tube  in  order  to  have  the 
flame  burn  quietly  at  the  top  of  the  burner  is  observed  by 
gradually  turning  off  the  supply  of  gas,  the  air-holes  being 
wide  open,  until  the  proportion  of  gas  and  air  in  the  tube  is 
such  as  to  cause  the  flame  to  strike  back  and  burn  at  the 
base  of  the  burner.  To  accentuate  the  change  in  position 
of  the  flame,  the  gas  should  again  be  turned  on  full  and  the 
character  of  the  flame  appearing  above  the  burner-tube 
noted.  By  means  of  a  pair  of  pliers  the  hot  burner-tube 
may  be  unscrewed,  as  before,  while  the  flame  is  still  burning. 


2.   Striking  back  of  a  Bunsen  flame.  —  The 

striking  back  of  a  Bunsen  flame  may  also  be 
shown  by  means  of  the  apparatus  (Fig.  133). 
(See  Ex.  6,  p.  345.) 

By  turning  on  a  good  supply  of  gas  it  is  easy 
to  get  a  perfect  Bunsen  flame  burning  at  the 
top  of  the  chimney.  Several  trials  will  prob- 
ably be  necessary  before  the  best  quantity  of  gas 
will  be  found.  When  the  proportions  of  gas 
and  air  entering  the  base  of  the  chimney  are 
correct,  a  great  blue  Bunsen  flame  will  be  ob- 
tained at  the  top.  By  turning  down  the  gas 
slowly  the  flame  will  strike  back  with  a  sharp, 
though  harmless  report,  and  burn  at  the  base 
of  the  burner. 

It  is  important  that  the  metal  part  of  the 
burner  should  not  be  allowed  to  become  too  hot 
by  burning  the  gas  at  the  base  of  the  chimney, 
for  the  hot  metal  increases  the  difficulty  of 
securing  a  well-formed  Bunsen  flame.  If  the 
metal  becomes  too  hot,  it  is  better  to  wait  a  few  minutes 
before  attempting  to  relight  the  burner.     As  most  Argand 


Fig.  133 


330 


CHEMICAL  LECTURE  EXPERIMENTS 


burners  have  a  small  gas-regulating  device  at  the  base,  the 
proportions  may  well  be  established  before  the  lecture,  and 
in  order  to  get  a  good  flame  it  will  only  be  necessary  to  open 
the  gas-cock  on  the  desk  and  light  the  gas. 

Argand  burner  and  chimney  (Fig.  133). 

3.  The  inner  portion  of  a  flame  is  cool.  —  (a)  A  striking 
demonstration  of  the  fact  that  the  inner  portion  of  a  flame 
is  cool  is  made  by  employing  a  burner  consisting  of  an  ordi- 
nary glass  funnel  5  cm.  across  the  top,  which  has  a  piece  of 
fine  copper  or  brass  gauze  over  the  mouth 
(Fig.  134).  The  stem  of  the  funnel  is 
connected  by  means  of  a  rubber  tube  to 
the  gas-cock.  A  small  heap  of  gunpowder, 
about  15  mm.  in  diameter,  is  placed  in  the 
centre  of  the  wire  gauze,  care  being  taken 
that  no  small  particles  of  the  powder  are 
scattered  on  the  gauze  away  from  the 
middle  of  the  heap.  After  protecting  the 
apparatus  from  strong  draughts,  the  gas 
is  turned  on  and  a  match  brought  down 
from  above  until  the  gas  is  ignited.  It 
burns  with  a  large  flame,  and  the  gun- 
powder remains  on  the  wire  gauze  uncon- 
sumed.  Ordinary  matches  may  be  thrust 
suddenly  through  the  flame,  and  their  heads  laid  on  the 
heap  of  gunpowder,  without  being  ignited.  On  slowly 
turning  down  the  gas,  the  flame  will  diminish  in  size  and 
soon  play  over  the  surface  of  the  gunpowder  and  cause  its 
ignition. 

In  repeating  the  experiment,  care  should  be  taken  to  allow 
the  gauze  covering  to  become  perfectly  cold,  and  in  no  case 
must  the  powder  be  added  from  the  bottle  or  other  container, 
but  rather  from  a  small  piece  of  paper.     In  introducing  the 


Fig.  1S4 


STRUCTURE   OF   FLAME  331 

phosphorus  matches,  care  should  be  taken  not  to  disturb 
the  heap  of  gunpowder  and  scatter  the  grains.  While  the 
explosion  of  such  a  small  quantity  of  gunpowder  is  not  dan- 
gerous, the  eyes  and  face  should  be  protected  from  any  pos- 
sible accident. 

5  cm.  funnel ;  fine  wire  gauze  ;  gunpowder  ;  shields  or  eye-glasses. 

(b)  A  pin  or  needle  is  thrust  through  a  match  just  below 
the  head.  On  allowing  the  match,  supported  on  the  needle, 
to  hang  down  the  tube  of  a  Bunsen  burner,  the  gas  may  be 
lighted  and  the  match  remain  unlighted  in  the  centre  of  the 
non-luminous  flame.  The  match,  to  avoid  touching  the  edge 
of  the  cone,  and  thereby  becoming  ignited,  should  be  so 
placed  that  it  is  as  near  as  possible  to  the  centre  of  the 
inner  cone.  A  Bunsen  burner  giving  a  perfect  flame  is 
necessary  for  this  experiment. 

4.  Pictures  of  flames  with  asbestos  paper.  —  An  interest- 
ing study  of  the  temperature  zones  of  an  ordinary  Bunsen 
flame  may  be  made  by  depressing  for  a  few  moments  a  piece 
of  paper  on  the  flame.  The  hotter  portions  of  the  flame  will 
soon  char  the  paper,  while  the  paper  in  the  cooler  zones  will 
not  become  darkened,  the  intensity  of  the  charring  showing 
the  intensity  of  the  heat.  It  will  thus  be  seen  that  the  cen- 
tre of  the  flame  is  comparatively  cool,  as  a  small  circle  7 
mm.  in  diameter  will  be  unburnt. 

The  most  satisfactory  paper  for  this  experiment  is  ordi- 
nary thin  asbestos  paper.  In  the  manufacture  of  this  paper 
certain  quantities  of  grease  or  oil  are  incorporated  with  the 
asbestos.  On  thrusting  the  paper  into  the  flame  the  heat 
chars  the  oil,  producing  a  blackening  of  the  paper,  and  one 
can  readily  determine,  by  noticing  the  intensity  of  the  color, 
the  relative  temperatures  of  different  parts  of  the  flame. 
Asbestos  paper  possesses  another  advantage,  i.e.,  it  is  not  com- 


332 


CHEMICAL   LECTURE   EXPERIMENTS 


bustible.     If  a  15  cm.  square  piece  of  thin  asbestos  paper  is 
held  vertically  in  the  flame,  a  remarkably  good  picture  of 

the  cross-section  of  the  flame 
may  be  obtained.  Some  slight 
degree  of  skill  is  necessary  to 
avoid  heating  the  paper  too 
hot,  and  thereby  charring  too 
much  of  it,  though  the  eye 
readily  perceives  when  the 
paper  should  be  withdrawn 
from  the  flame.  Pictures  of 
the  flame  in  almost  any  posi- 
tion may  be  made  by  using 
this  paper  (Fig.  135). 


'i 

c 

Fig.  135 


5.  Pictures  of  a  flame  on  metallic  copper.  —  The  beauti- 
ful colors  formed  in  the  oxidation  of  copper  may  be  advan- 
tageously used  to  form  a  picture  of  a  Bunsen  flame. 

A  20  cm.  square  of  thinnest  sheet  copper  is  carefully 
cleaned  and  polished.  The  sheet  is  then  held  in  the  Bun- 
sen  flame,  as  described  in  the  preceding  experiment.  Im- 
mediately the  copper  will  take  on  in  colors  the  outline  of 
the  flame,  but  on  account  of  the  metaPs  great  conductivity 
of  heat,  the  sheet  must  be  heated  for  only  a  few  moments. 

In  case  the  experiment  is  to  be  repeated,  the  picture  can 
be  instantly  effaced  by  washing  with  a  few  drops  of  potas- 
sium dichromate  solution  to  which  some  sulphuric  acid  has 
been  added. 

Pictures  of  the  flame  in  numerous  positions  can  be  readily 
obtained  by  this  method. 

Thin  sheet  copper  ;  K2Cr207  solution. 


6.   Ignition  of  the  gas  arising  from  a  recently  extinguished 
candle.  —  That  the  candle  flame  is  due  chiefly  to  the  burn- 


STRUCTURE   OF   FLAME 


333 


ing  of  the  gas  formed  by  the  action  of  heat  on  the  solid 
portion  is  shown  by  blowing  out  the  candle  and  holding 
the  match  1  or  2  cm.  above  the  wick,  when  it  will  be  seen 
that  the  gas  or  smoke  rising  from  the  wick  will  catch  fire 
and  run  back,  communicating  its  flame  to 
the  wick.  To  show  the  ignition  of  the 
gas  more  strikingly,  the  candle  is  placed 
inside  of  an  ordinary  Argand  lamp  chim- 
ney (Fig.  136).  The  chimney  must  be 
raised  from  the  table  to  allow  a  good 
current  of  air  to  enter,  and  sufficient  air 
must  be  furnished  to  allow  the  candle 
to  burn  steadily.  On  blowing  out  the 
candle  the  gas  will  rise,  and  a  match 
held  at  the  top  of  the  chimney  will  set 
fire  to  the  gas  and  ultimately  to  the  can- 
dle as  described  above.  It  is  not  unusual 
to  have  the  flame  descend  some  6  or  8  cm. 
to  the  wick.  Instead  of  a  match  a  flame  from  a  blowpipe 
jet  or  a  glass  tip  may  be  directed  across  the  top  of  the 
chimney,  and  the  distance  from  the  top  of  the  chimney  to 
the  top  of  the  wick  measured  as  the  distance  that  the  flame 
has  travelled. 

Argand  lamp  chimney ;  candle. 


Fig.  136 


■^^^ 


M. 


Fig.  137 


7.   Collection  of  combustible  gases 
from  the  interior  of  a  candle  flame. 

—  A  300  cc.  glass  cylinder  is  fitted 
with  a  two-holed  rubber  stopper  car- 
rying a  short  glass  elbow  and  a  long 
glass  tube  reaching  to  the  bottom  of 
the  cylinder  and  bent  over  on  the 
outside  so  as  to  descend  to  the  wick 
of  a  wax  candle  (Fig.   137).      The 


334  CHEMICAL   LECTUEE   EXPERIMENTS 

candle  is  so  held  that  the  tip  of  the  wick  just  touches  the 
end  of  the  long  glass  tube.  On  lighting  the  candle  and 
applying  a  gentle  suction  to  the  glass  elbow,  the  unburned 
gases  generated  by  the  heat  of  the  candle  are  drawn  over 
into  the  cylinder.  After  a  few  moments,  sufficient  gas  will 
have  been  collected  to  burn  when  the  cork  is  removed  and  a 
flame  applied.  If  the  cylinder  is  not  completely  filled  with 
the  gas,  enough  air  may  remain  to  cause  a  slight  explosion. 

300  cc.  cylinder  ;  suction-pump  ;  candle. 

8.  Cooling  a  Bunsen  flame  with  wire  gauze. — When  a 
Bunsen  flame  is  allowed  to  play  upon  a  piece  of  wire  gauze, 
the  heat  is   conducted  from  the  flame  along  the  wire  so 

rapidly  as  to  prevent  the  gas  that  rises  through 
the  meshes  from  being  ignited. 

A  piece  of  wire  gauze  is  suddenly  depressed 
on  the  top  of  the  inner  cone  of  a  Bunsen  flame. 
The  flame  will  remain  entirely  on  the  lower  side 
of  the  gauze,  though  in  a  few  moments,  as  the 
wire  becomes  heated,  an  ignition  of  the  gas 
above  the  gauze  results. 

The  experiment  may  be  varied  by  turning  on 
the  gas  without  lighting  it,  holding  a  piece  of 
wire  gauze  horizontally  about  4  cm.  above  the 

'- ^     top  of  the  burner,  and  applying  a  flame  from 

above.  The  gas  will  burn  on  top  of  the  gauze, 
and  it  will  be  impossible  to  generate  sufficient  heat  to  ignite 
the  gas  below  (Fig.  138). 

This  cooling  effect  of  wire  gauze  finds  practical  use  in  the 
Davy  safety-lamp. 

9.  The  Davy  safety-lamp.  —  The  use  of  the  Davy  safety- 
lamp  in  the  presence  of  explosive  gaseous  mixtures  is  well 
illustrated  by  lowering  it  into  a  mixture  of  ether  vapor  and 
air. 


STRUCTURE  OF   FLAME  335 

A  2  1.  beaker  is  used  to  hold  the  explosive  mixture  ob- 
tained by  pouring  5  cc.  of  ether  vapor  into  the  beaker  and 
then  covering  its  mouth  with  a  cardboard  cover.  A  Davy 
lamp  is  lighted  (care  being  taken  that  the  flame  is  not  too 
high)  and  carefully  lowered  into  the  beaker.  As  it  comes 
in  contact  with  the  gaseous  mixture,  a  flame  may  be  seen 
playing  for  a  few  seconds  inside  the  wire  gauze  surrounding 
the  lamp.  As  the  lamp  is  lowered,  the  flame  is  extin- 
guished, owing  to  the  deficiency  in  oxygen,  and  the  gaseous 
mixture  is  not  ignited. 

2  1.  beaker  ;  cardboard  cover ;  Davy  safety -lamp  ;  ether. 

10.  Increased  illumination  of  a  Bunsen  flame  by  the  intro- 
duction of  particles  of  carbon.  —  (a)  The  incandescence  of 
small  particles  of  carbon  which  are  caused  to  pass  through 
a  Bunsen  flame  renders  it  luminous. 

The  simplest  method  of  introducing  the  particles  of 
carbon  is  to  rub  together  two  pieces  of  charcoal  near  the 
air-holes  at  the  base  of  the  burner.  The  fine  charcoal  dust 
will  be  drawn  up  into  the  tube  and  cause  the  flame  to 
become  luminous. 

Two  pieces  of  charcoal. 

(6)  By  introducing  very  finely  divided  carbon  into  a 
colorless  Bunsen  flame  a  luminous  flame  is  obtained.  An 
extremely  finely  divided  form  of  carbon  is  obtained  as  lamp- 
black from  the  flame  of  burning  turpentine,  and  if  a  current 
of  air  ladened  with  the  soot  from  a  flame  of  this  nature  is 
conducted  into  a  Bunsen  flame,  the  flame  is  rendered  lumi- 
nous. 

Turpentine  is  burned  in  a  small  lamp  made  by  thrusting 
a  short  piece  of  glass  tubing  into  a  cork,  having  a  slit  cut 
in  one  side,  fitting  the  mouth  of  a  small  bottle.  A  piece  of 
round  cotton  wick  is  drawn  through  the  glass  tube,  and  the 


336 


CHEMICAL   LECTURE   EXPERIMENTS 


bottle  is  one-half  filled  with  turpentine.  On  lighting  the 
free  end  of  the  wick,  a  small  smoky  flame  will  be  obtained. 
A  12  cm.  length  of  combustion-tubing  is 
so  clamped  that  it  serves  as  a  chimney 
to  deflect  the  products  of  combustion  into 
....  the  lower  part  of  a  Bunsen  flame.     The 

Ij  column  of  soot  rising  through  the  com- 

'  "^  bustion-tube  enters  the  Bunsen  flame  and 

there  becomes  heated  to  incandescence. 

The  products  of  the  incomplete  com- 
bustion of  a  candle  may  be  condvicted 
, — 4-''  [       into  the  base  of  a   Bunsen  burner   by 

rr  ^^"^^  I  means  of  a  glass  elbow  thrust  into  one 
of  the  air-holes  (Fig.  139).  On  lighting 
the  Bunsen  burner,  sufficient  draft  will 
be  obtained  to  conduct  the  products  of 
combustion  of  a  burning  candle,  the  tip 
of  whose  wick  is  thrust  into  the  lower 
end  of  the  glass  elbow,  up  into  the  .Bunsen  flame.  The 
flame  is  rendered  luminous. 

Turpentine  lamp ;  12  cm.  length  of  combustion- tubing ;  glass  elbow  ; 
candle. 


Fig.  139 


11.  Carburetting  a  flame  of  hydrogen.  — The  introduction 
of  solid  particles  of  carbon  into  a  non-luminous  flame  may 
be  effected  by  introducing  vapors  of  carbon  compounds 
which  are  decomposed  readily  by  heat,  liberating  finely 
divided  carbon. 

A  current  of  hydrogen  is  conducted  through  a  test-tube 
containing  some  cotton-batting  and  fitted  with  a  three-holed 
cork  (Fig  140).  In  one  hole  is  a  glass  elbow,  extending  to 
the  bottom  of  the  test-tube,  through  which  the  hydrogen 
enters.  The  hydrogen  issues  through  a  bent  glass  tube 
serving  as  a  jet  in  another  hole.     A  small  dropping-funnel 


STRUCTURE   OF   FLAME 


337 


containing  benzine  is  fitted  in  the  third  hole.  After  all  air 
is  driven  out  of  the  apparatus,  the  hydrogen  is  ignited  at 
the  jet,  where  it  burns  with  a  non-luminous 
flame.  A  platinum  tip  should  be  used.  On 
opening  the  stop-cock  of  the  dropping-fumiel 
and  allowing  a  few  drops  of  benzine  to  fall  . 
upon  the  cotton,  the  flame  immediately  be- 
comes luminous.  The  benzine  vapor  carried 
along  with  the  hydrogen  is  decomposed  by 
the  hot  hydrogen  flame,  setting  free  carbon, 
a  part  of  which  becomes  heated  to  incan- 
descence. The  actual  liberation  of  carbon 
is  proved  by  the  soot  deposited  on  a  cold 
porcelain  dish  depressed  upon  the  luminous 
flame.  A  dish  depressed  upon  the  hydrogen 
flame  produces  no  deposit. 

A  similar  apparatus  may  be  used  to  illustrate  the  car- 
buretting  of  ordinary  coal  gas,  in  which  case,  however,  it 
is  better  to  replace  the  platinum  tip  by  a  regular  gas-burner. 
Coal  gas  issuing  from  a  jet  saturated  with  benzine  vapor 
burns  with  a  much  more  luminous  flame  than  the  uncar- 
buretted  gas,  as  may  be  readily  seen  by  holding  an  ordinary 
gas-flame  beside  it. 

Large  test-tube  ;  three-holed  cork  ;  dropping-funnel ;  cotton-batting  ; 
Pt  jet ;  H  supply  ;  benzine. 


12.  Luminosity  of  a  Bunsen  flame  increased  by  finely 
divided  nickel.  —  In  Ex.  9,  p.  418,  carbon  monoxide,  satu- 
rated with  the  vapor  of  nickel  tetracarbonyl,  is  conducted 
into  the  air-holes  of  a  Bunsen  burner.  The  vapor  mixes 
with  the  illuminating  gas,  and  the  heat  of  the  flame  is 
sufficient  to  decompose  the  tetracarbonyl,  setting  free  finely 
divided  nickel  which  is  burned  in  the  flame,  imparting  to  it 
an  intense  luminosity. 

Waste  gases  from  Ex.  9,  p.  416. 


338 


CHEMICAL  LECTURE  EXPERIMENTS 


Fig.  141 


13.  Increase  in  brilliancy  of  a  non-luminous  flame  by  heat- 
ing.—  A  piece  of  platinum  foil,  at  least  15  cm.  long,  is 
rolled  in  the  form  of  a  tube,  bound  with  some  pieces   of 

platinum  wire,  and  slipped  over  the 
end  of  a  Bun  sen  burner,  forming  an 
extension  to  its  main  tube.  The 
burner  is  clamped  in  an  inclined 
position,  and  on  opening  the  air- 
holes at  the  base,  the  flame  is  so 
regulated  as  to  appear  just  non- 
luminous  at  the  top  (Fig.  141).  On 
heating  the  platinum  tube  with  a 
strong  burner,  the  issuing  gas  at 
the  end  of  the  platinum  tube  will 
be  seen  to  have  acquired  a  decided  luminosity.  It  is  advis- 
able to  heat  the  platinum  thoroughly  before  using  it  for 
this  experiment,  in  order  to  burn  off  all  dust,  which  would 
otherwise  color  the  flame. 

Platinum  foil  15  cm.  long, 

14.  Luminosity  of  a  flame  decreased  by  dilution  with  an 
indifferent  gas.  —  Illuminating  gas,  when  diluted  with  carbon 
dioxide,  loses  its  illuminating  power. 

Carbon  dioxide  from  a  Kipp  generator  is  introduced  into 
one  of  the  air-holes  in  the  base  of  a  Bunsen  burner  by  means 
of  a  small  cork  and  a  glass  tube  (Fig.  139).  The  other  air- 
hole is  closed  with  a  cork.  Illuminating  gas  is  conducted 
through  the  burner  and  ignited  at  the  top,  where  it  burns 
with  a  flickering,  luminous  flame.  Carbon  dioxide  is  then 
slowly  admitted,  with  the  result  that  the  flame  diminishes 
in  luminosity  until  finally  it  becomes  blue. 

The  same  effect  may  be  obtained  by  using  the  chromium 
oxychloride-hydrogen,  in  place  of  the  illuminating-gas, 
flame. 


RECIPROCAL   COMBUSTION  339 

By  heating  the  diluted  gas  with  the  platinum  extension- 
tube  of  Ex.  13,  the  luminosity  may  again  be  restored. 

Bunsen  burner  with  cork  and  tubes  in  air-hole  ;  CO2  generator  ;  Pt 
tube  (Ex.  13). 

15.   Effect  of  the  dilution  of  air  on  a  luminous  flame. — 

The  diminution  in  luminosity  in  a  flame,  resulting  from  the 
dilution  of  the  combustible  gas  by  an  indifferent  gas,  may 
also  be  obtained  by  diluting  the  atmosphere  with  a  non- 
combustible  gas  such  as  carbon  dioxide.  An  artificial 
atmosphere,  containing  one-third  carbon  dioxide,  is  pre- 
pared by  filling  two-thirds  of  a  large  bottle  with  air  and 
the  remaining  volume  with  carbon  dioxide.  Illuminating 
gas  is  conducted  through  the  recurved  jet  (Fig.  41,  p.  85) 
and  ignited.  A  luminous  flame,  3  or  4  cm.  high,  is  ob- 
tained, and  the  jet  is  lowered  into  the  artificial  atmos- 
phere of  air  and  carbon  dioxide.  The  luminosity  of  the 
flame  disappears,  though  by  withdrawing  the  jet  it  can  be 
seen  that  the  gas  has  not  been  extinguished. 

Hydrogen,  burning  from  the  recurved  jet  having  a  plati- 
num tip  on  which  a  small  amount  of  sodium  chloride  solu- 
tion has  been  placed,  burns  in  the  air  with  a  brilliant  yellow 
flame.  When  lowered  into  the  diluted  atmosphere,  the 
luminosity  disappears. 

A  candle  lowered  into  such  an  atmosphere  is  immediately 
extinguished. 

Large  bottle  containing  one-third  CO2,  two-thirds  air ;  jet  (Fig.  41 , 
p.  85) ;  NaCl  solution  ;  H  generator  ;  candle  on  wire. 

RECIPROCAL   COMBUSTION 

1.   Combustion   of   oxygen  in  hydrogen.  —  (a)   A  jet  of 

oxygen  will  burn  as  well  in  an  atmosphere  of  hydrogen 
as  a  jet  of  the  latter  gas  will  burn  in  the  presence  of  air  or 


340  CHEMICAL   LECTURE   EXPERIMENTS 

oxygen.  That  the  terms  "  combustible  "  and  '^  supporter  of 
combustion  "  are  only  relative  is  well  shown  by  an  experi- 
ment in  which  oxygen,  ordinarily  considered  non-combusti- 
ble, burns  in  an  atmosphere  of  hydrogen  which  extinguishes 
the  flame  of  a  candle. 

A  liter  cylinder  filled  with  hydrogen  is  held  mouth  down- 
wards and  the  gas  ignited  at  its  mouth.  A  slow  stream  of 
oxygen  is  passed  through  a  glass  tube  which  is  carefully 
thrust  up  into  the  jar  of  hydrogen  (Fig.  42,  p.  85).  As 
the  tip  of  the  glass  tube  passes  the  burning  gas  the  oxygen 
is  ignited.  If  a  small  platinum  tip  is  provided,  the  flame 
will  be  seen  to  be  colorless.  If  the  oxygen  tube  is  with- 
drawn, the  flame  will  be  extinguished  as  soon  as  it  leaves 
the  atmosphere  of  hydrogen.  The  tube  is  again  introduced, 
and  the  gas  will  continue  to  burn  until  the  hydrogen  is  con- 
sumed. To  prevent  the  possibility  of  the  formation  of  an 
explosive  gaseous  mixture,  care  must  be  taken  that  the  oxy- 
gen flame  is  not  extinguished  by  accidental  pressure  on  the 
rubber  tube  conducting  the  oxygen.  Should  the  flame  be 
extinguished,  the  glass  tube  must  be  immediately  withdrawn 
and  the  jar  refilled  with  hydrogen,  after  expelling  all  the 
remaining  gas. 

Liter  cylinder  of  hydrogen  ;  current  of  oxygen, 

(6)  The  liter  cylinder  of  hydrogen  may  be  advantageously 
replaced  by  an  apparatus  for  furnishing  a  constant  supply 
of  hydrogen.  The  simplest  form  of  apparatus  consists 
of  a  small  lamp  chimney  vertically  clamped  with  a  one- 
holed  cork  fitted  into  the  upper  end.  A  slow  stream  of 
hydrogen  is  passed  through  a  glass  tube  in  this  cork,  and  the 
gas  lighted  at  the  lower  end  of  the  chimney.  The  glass  tube 
conducting  the  oxygen  is  now  thrust  into  the  lamp  chimney 
from  below,  with  all  the  precautions  described  above. 

Kipp  H  generator ;  lamp  chimney  ;  current  of  oxygen. 


RECIPROCAL   COMBUSTION 


341 


2.  Continuous  combustion  of  oxygen  in  hydrogen.  —  Oxy- 
gen may  be  made  to  burn  continuously  in  an  atmosphere 
of  hydrogen  by  means  of  the  apparatus,  Fig. 
142. 

Hydrogen  is  conducted  through  the  elbow 
in  the  cork  at  the  bottom  of  the  lamp  chim- 
ney, and  is  ignited  at  the  opening  in  the  cover 
at  the  top.    A  long  glass  elbow,  which  may  be 
easily  raised  and  lowered,  is  thrust  through 
the  second  hole  in  the  cork  until  the  end  is 
just  on  a  level  with  the  cover.     After  hydro- 
gen has  displaced  all  air  in  the  apparatus, 
and  has  been  lighted  as  it  issues  from  the 
top,   a   gentle   current   of   oxygen   is   passed 
through  the  long  glass  elbow,  and  is  seen  to  _^      J) 
burn  in  the  interior  of  the  hydrogen  flame.        -p^^  ^^2 
The  tube  may  be  then  slowly  lowered,  and  it 
will  be  seen  that  the  oxygen  burns  in  the  atmosphere  of 
hydrogen.     As  the  heat  of  this  flame  is  very  intense  and 
is  liable  to  melt  the  glass,  it  is  advisable  to  provide   for 
the  glass  tube  a  platinum  tip,  such  as  is  described  in  Ex.  5, 
p.  183. 

The  greatest  precaution  must  be  exercised  to  prevent  the 
formation  of  a  gaseous  explosive  mixture  in  the  interior  of 
the  lamp  chimney ;  and  in  case  the  inner  flame  is  extin- 
guished by  accidental  pressing  or  kinking  of  the  rubber  tube, 
the  oxygen  supply  must  be  immediately  cut  off,  as  otherwise 
a  dangerous  explosion  might  easily  occur. 


Apparatus  (Fig.  142) 
supply. 


lamp  chimney  ;  cork  and  tubes ;  H  and  O 


3.  Combustion  of  air  in  illuminating  gas.  —  A  simple 
apparatus  for  showing  this  phenomenon  consists  of  an 
Argand  lamp  chimney  (Fig.  143)  fitted  with  a  large  cork,  car- 


1 


-.^ 


342  CHEMICAL   LECTURE   EXPERIMENTS 

Tying  a  small  elbow  and  a  10  cm.  length  of  combustion-tubing. 
The  combustion-tubing  should  be  provided  with  a  platinum 
tip,  made  by  rolling  a  piece  of  platinum  foil  in 
such  a  manner  that  it  will  snugly  fit  the  interior 
of  the  tube.  The  chimney  is  then  clamped  in 
an  upright  position  with  the  open  end  upper- 
most, and  a  cover  of  thick  asbestos  card,  or 
better,  a  brass  cap,  is  fitted  on  the  top  of  the 
chimney.  A  2  cm.  opening  should  be  made  in 
the  centre  of  the  cap. 

On  closing  the  opening  in  the  cap  and  ad- 
mitting illuminating  gas  through  the  elbow, 
the  air  in  the  lamp  chimney  is  soon  driven  out, 
and  the  gas  may  be  ignited  as  it  issues  from 
the  lower  end  of  the  combustion-tube.  On  opening  the 
orifice  in  the  cap,  the  gas  rises  and  the  flame  recedes  through 
the  combustion-tube,  and  appears  at  the  platinum  jet  inside 
the  chimney.  The  escaping  gas  may  be  lighted  at  the  top 
of  the  chimney  and  there  simultaneously  appears  a  flame  of 
gas  burning  in  air  and  a  flame  of  air  burning  in  gas.  It 
may  be  necessary  to  choke  the  piece  of  combustion-tubing 
by  means  of  a  small  cork  with  a  slit  cut  in  one  side,  to  pre- 
vent too  large  a  volume  of  air  from  entering  the  chimney 
through  the  tube.  By  properly  regulating  the  supply  of 
coal  gas  and  the  admission  of  air,  a  flame  2  or  3  cm.  high 
is  easily  obtained. 

While  the  two  flames  do  not  appear  markedly  different,  it 
will  be  found  on  thrusting  a  piece  of  paper  or  a  visiting 
card  on  the  end  of  a  wire  through  the  opening  at  the  top  of 
the  chimney  into  the  inner  flame,  that  only  that  portion  of 
the  card  will  be  burned  which  is  actually  in  the  flame  itself. 
By  carefully  inserting  the  card,  a  picture  of  the  flame  may 
be  obtained  by  charring  the  card. 

Apparatus  (Fig.  143) ;  lamp  chimney  ;  corks  and  tubes  ;  asbestos  or 
brass  cap. 


RECIPROCAL   COMBUSTION 


343 


4.  Combustion  of  air  in  hydrogen. — By  using  an  apparatus 
similar  to  that  shown  in  Fig.  143,  in  which,  however,  the 
large  glass  tube  in  the  cork  has  a  U  rather  than  a  straight 
form,  the  combustion  of  air  in  hydrogen  may  be  well 
studied.      The   apparatus    is    shown   in 

Fig.  144,  and  consists  of  a  lamp  chim- 
ney provided  with  a  two-holed  cork  at 
the  bottom,  carrying  a  small  glass  elbow 
and  a  large  U-tube  1  cm.  in  diameter. 
Each  end  of  the  U-tube  should  be  pro- 
vided with  a  platinum  tip  (Ex.  3).  A 
cork  should  be  inserted  in  the  top  of 
the  chimney  and  hydrogen  admitted. 
After  all  the  air  is  expelled,  the  hydro- 
gen escaping  from  the  outer  limb  of  the 
U-tube  is  ignited.  On  removing  the  cork 
from  the  top  of  the  chimney,  the  flame  recedes  through  the 
U-tube,  and  soon  appears  burning  at  the  other  end  inside  the 
chimney  as  a  flame  of  air  burning  in  an  atmosphere  of  hydro- 
gen. On  again  inserting  the  cork  in  the  top  of  the  chimney, 
the  hydrogen  will  escape  through  the  U-tube,  and  the  flame 
recede  and  appear  as  a  jet  of  burning  hydrogen  at  the  outer 
end  of  the  U-tube.  The  operation  may  be  repeated  as  often 
as  is  desired.  The  best  results  are  obtained  when  the  flame 
at  the  open  end  of  the  U-tube  is  not  more  than  1  or  2  cm. 
high. 

The  operation  is  even  more  satisfactory  when  illuminating 
gas  is  used  in  place  of  hydrogen,  since  it  has  the  advantage 
of  giving  a  luminous  flame. 

Apparatus  (Fig.  144) ;  lamp  chimney;  large  U-tube ;  corks  ;  H  supply. 

5.  Reciprocal  combustion  of  illuminating  gas  and  air. — 

An  interesting  modification  of  the  experiment  illustrating 
the  relative  combustibility  of  gas  and  air  is  made  by  means 


344 


CHEMICAL   LECTURE   EXPERIMENTS 


of  the  apparatus  (Fig.  145).  An  ordinary  lamp  chimney  is 
fitted  with  a  two-holed  cork  carrying  a  glass  elbow  and  a 
glass  tube,  7  mm.  internal  diameter.  The 
cork  is  clamped  in  a  vertical  position  and 
illuminating  gas  is  conducted  through  the 
small  glass  elbow  and  ignited.  The  chim- 
ney is  then  placed  over  the  cork.  The  flame 
will  continue  to  burn,  a  liberal  supply  of 
air  entering  the  lamp  chimney  through  the 
large  glass  tube.  On  turning  on  more  gas, 
however,  the  flame  will  soon  ascend  and 
burn  at  the  asbestos  cover  on  the  upper 
part  of  the  chimney,  while  a  current  of  air 
drawn  through  the  large  glass  tube  will 
burn  at  the  end  of  the  tube  inside  the 
chimney.  A  small  glass  tube  is  drawn  out 
to  a  long,  fine  jet,  through  which  illumi- 
nating gas  is  conducted  and  allowed  to  burn. 
The  small  flame  of  burning  illuminating 
gas  may  then  be  thrust  through  the  large  tube  into  the 
centre  of  the  flame  of  air  burning  in  the  chimney.  The 
illuminating  gas  will  still  continue  to  burn,  and  there  is 
simultaneously  obtained  a  flame  of  illuminating  gas  burn- 
ing at  the  top  of  the  chimney  in  the  air,  a  flame  of  air 
burning  in  illuminating  gas  inside  the  chimney,  and  a  flame 
of  illuminating  gas  burning  inside  the  flame  of  air.  That 
this  last  flame  will  burn  only  in  air  is  seen  by  thrusting  the 
glass  tube  through  the  air  flame  into  the  atmosphere  of 
illuminating  gas.  On  withdrawing  the  tube  the  gas  is 
again  ignited  and  continues  to  burn  in  the  air.  It  is 
important  that  the  long,  fine  tube  be  of  small  diameter,  as 
a  large  tube  will  so  obstruct  the  passage  of  air  as  to  make 
it  impossible  to  secure  a  good  flame.  If  the  illuminating 
gas  admitted  through  the  glass  elbow  is  now  slowly  turned 


Fig.  145 


RECIPROCAL   COMBUSTION 


345 


off,  the  flame  at  the  top  of  the  chimney  will  diminish  in 
size  and  finally  recede  into  the  chimney  and  burn  at  the 
end  of  the  glass  elbow  as  at  first. 

Apparatus  (Fig.  145) ;  lamp  chimney ;  asbestos  disk  with  2  cm. 
hole  ;  cork  and  tubes ;  long  glass  jet. 

6.  Combustion  of  air  in  illuminating  gas.  —  By  means 
of  the  apparatus  (Fig.  146)  the  combustion  of  air  in  illumi- 
nating gas  may  be  very  easily  shown. 

An  Argand  gas-burner  is  provided  with  a 
large  chimney,  such  as  is  shown  in  the  figure. 
This  form  of  chimney  is  not  designed  for  use 
on  an  Argand  gas-burner,  but  the  constriction 
just  above  the  flame  makes  it  especially  desir- 
able in  connection  with  this  experiment.  A 
piece  of  sheet  copper  or  galvanized  iron,  with 
a  7  mm.  hole  in  the  centre,  is  laid  over  the  top 
of  the  chimney  after  the  gas  is  lighted  and 
burning  with  a  flame  approximately  2  cm.  high. 
When  the  disk  is  placed  over  the  chimney,  the 
gas  smokes  inside  the  chimney,  the  flame  re- 
cedes, and  may  be  seen  to  be  burning  at  the 
central  air-draft  instead  of  at  the  ring  where 
the  gas  issues  through  the  burner. 

By  regulating  the  supply  of  gas,  a  flame  some 
1  or  2  cm.  high  may  be  obtained.  The  gas  issu- 
ing from  the  hole  in  the  disk  may  be  lighted, 
and  it  will  burn  with  a  feebly  luminous  flame. 

It  is  thus  possible  to  have  a  flame  of  air  burning  in  illu- 
minating gas  at  the  base  of  the  burner  and  a  flame  of  gas 
burning  in  air  at  the  top.  This  is  one  of  the  simplest  meth- 
ods of  showing  the  phenomenon  of  reciprocal  combustion. 

Argand  burner  and  chimney  (Fig.  146) ;  copper  or  galvanized  iron 
disk  with  7  mm.  hole  in  centre. 


Fig.  146 


346  CHEMICAL   LECTURE   EXPERIMENTS 

7.  Combustion  of  oxidizing  agents  in  an  atmosphere  of 
hydrogen.  — A  number  of  substances  furnishing  a  supply  of 
oxygen  may  be  made  to  burn  in  an  atmosphere  of  hydrogen. 
The  hydrogen  is  held  in  a  liter  bell-jar  clamped  mouth 
downwards,  or  use  may  be  made  of  a  lamp  chimney  through 
which  a  stream  of  hydrogen  is  sent  from  the  top,  issuing  at 
the  bottom.  Potassium  chlorate  is  placed  in  a  small  porce- 
lain crucible  suspended  in  the  loop  of  a  stout  iron  wire 
long  enough  to  extend  up  into  the  jar  or  lamp  chimney. 
The  potassium  chlorate  is  then  melted  and  strongly  heated. 
When  oxygen  begins  to  be  liberated  it  is  suddenly  thrust 
through  the  burning  hydrogen  at  the  mouth  of  the  bell-jar 
or  lamp  chimney.  The  salt  will  burn  with  intense  bril- 
liancy with  the  characteristic  color  of  potassium  salts.  By 
the  use  of  strontium  or  barium  chlorates  the  flame  will  be 
colored  respectively  red  and  green.  An  intense  yellow 
flame  may  be  obtained  by  using  a  mixture  of  four  parts 
potassium  chlorate  and  one  part  sodium  nitrate. 

Nitric  and  iodic  acids,  both  rich  in  oxygen,  burn  in  an 
atmosphere  of  hydrogen  when  heated.  A  small  quantity  of 
fuming  nitric  acid  is  placed  in  a  crucible  and 
heated  to  boiling.  Without  waiting  long  enough 
to  allow  much  of  the  oxides  of  nitrogen  to  es- 
cape, the  crucible  is  thrust  into  the  atmosphere 
of  hydrogen,  where  it  will  burn.  A  small  quan- 
tity of  iodic  acid  placed  in  a  crucible  and  heated 
very  hot  will  burn  on  being  introduced  into  the 
hydrogen  atmosphere,  large  quantities  of  iodine 
being  liberated  and  deposited  on  the  walls  of 
the  jar. 

As  the  intense  heat  of  the  hydrogen  burning 
at  the  mouth  of  the  jar  or  lamp  chimney  is  likely  to  break 
the  glass  on  long-continued  heating,  it  is  advisable  to  pass 
the  hydrogen  through  the  bottom  of  an  ordinary  Argand 


RECIPROCAL   COMBUSTION  347 

lamp  chimney  clamped  in  a  vertical  position,  fitted  with  a 
one-holed  cork  and  a  glass  elbow  at  the  bottom,  and  covered 
at  the  top  with  a  disk  of  thick  asbestos  with  a  2  cm.  open- 
ing in  the  centre  (Fig.  147).  In  this  form  of  apparatus 
the  hydrogen  burns  at  the  opening  of  the  asbestos,  caus- 
ing no  undue  heating  of  the  glass.  The  materials  to  be 
introduced  into  the  hydrogen  atmosphere  must,  however, 
be  held  in  a  crucible  suspended  from  a  long  iron  wire 
capable  of  being  lowered  through  this  opening. 

Lamp  chimney  ;  H  generator  ;  deflagrating-spoon  ;  apparatus  (Fig. 
147);  asbestos  disk  ;  KCIO3  ;  Ba(C103)2  ;  81(0103)2;  NaNOs  ;  fuming 
HNO3 ;  I2O5. 


.•^# 


METALS 


The  division  of  the  elements  into  the  two  groups,  non- 
metals  and  metals,  though  more  or  less  arbitrary,  is  here 
made  in  the  customary  manner. 

The  size  of  this  book  will  not  permit  of  an  exhaustive 
list  of  experiments  on  the  metals,  and  hence  those  here 
selected  are  to  be  looked  upon  only  as  suggestive  additions 
to  the  usual  precipitations. 


348 


?C 


\"- 


SODIUM 


1.  Metallic  lustre. — Metallic  sodium,  as  ordinarily  ob- 
tained in  the  market,  is  covered  with  a  crust,  and  the  metal 
must  be  cut  in  order  to  show  the  metallic  lustre. 

A  piece  of  the  metal  is  laid  on  dry  filter-paper  to  remove 
the  excess  of  naphtha  and  then  cut  with  a  knife.  The 
freshly  cut  surface  shows  the  bright  metallic  lustre  of  this 
element,  but  almost  immediately,  i.e.,  in  a  very  few  seconds, 
becomes  covered  with  a  tarnish. 

A  piece  of  sodium  from  which  the  thick  outer  crust  has 
been  removed  may  be  freed  from  all  tarnish  by  immersing 
it  for  a  few  moments  in  absolute  alcohol.  The  sodium  re- 
acts with  the  alcohol  somewhat,  and  the  outer  surface  is 
entirely  freed  from  oxides.  The  piece  of  sodium  must  then 
be  thrust  under  naphtha,  where  its  lustre  will  be  preserved 
for  some  time. 

Absolute  alcohol ;  naphtha ;  Na. 

2.  Melting  the  metal.  —  Sodium  may  be  readily  melted  if 
several  small  pieces  are  heated  under  kerosene  in  a  large, 
dry  test-tube.  The  metal  melts  at  94°  C.  to  a  silver-colored 
liquid,  which  preserves  its  lustre  for  some  time  if  well 
covered  with  kerosene. 

If  the  test-tube  is  allowed  to  become  cold,  the  metal  solid- 
ifies, taking  the  form  of  the  interior  of  the  tube. 

Large,  dry  test-tube  ;  kerosene  ;  Na. 

349 


350 


CHEMICAL   LECTURE   EXPERIMENTS 


^ 

^ 

: 

1 

^ 

^ 

r                  >i 

3.  Action  of  sodium  on  water.  —  The  action  of  sodium  on 
water  with  the  liberation  of  hydrogen  and  the  formation  of 
sodium  hydroxide  is  best  shown  by  means  of  the  apparatus 
(Fig.  148).  A  glass  tube,  20  cm.  long 
and  9  to  10  mm.  internal  diameter,  is 
clamped  in  a  vertical  position  with  its 
lower  end  dipping  3  cm.  below  the  sur- 
face of  water  in  a  300  cc.  cylinder.  The 
water  should  about  three-fourths  fill  the 
cylinder  and  should  contain  a  few  drops 
of  phenol-phthalein  solution.  A  piece 
of  sodium  is  pressed  into  a  spherical 
mass  not  more  than  4  mm.  in  diameter. 
In  preparing  this  pellet  of  sodium  it  is 
important  that  the  hands  should  not  be 
wet  or  too  moist  from  X3erspiration.  On 
dropping  the  sodium  into  the  vertically 
clamped  tube  the  decomposition  of  the 
water  is  immediately  effected,  and  in  a  few  moments  hydro- 
gen may  be  ignited  at  the  upper  end  of  the  tube.  The 
sodium  hydroxide  obtained  in  the  reaction,  being  heavier 
than  water,  settles  to  the  bottom  of  the  cylinder  in  currents 
and,  by  reason  of  its  alkalinity,  imparts  a  strong  color  to 
the  phenol-phthalein  solution. 

If  care  is  taken  to  prepare  a  spherule  of  sodium,  it  will 
remain  in  the  centre  of  the  cup  formed  on  the  surface  of 
the  water  by  the  capillarity  of  the  tube  and  regularly  evolve 
hydrogen.  At  times,  however,  especially  if  the  sodium 
is  not  spherical  in  form  or  if  the  interior  of  the  glass 
tube  is  wet  above  the  level  of  water  in  the  cylinder,  the 
sodium  will  stick  to  the  glass,  and  a  slight  explosion  will 
occur. 

Apparatus  (Fig.  148)  ;  20  cm.  length  glass  tube  10  mm.  diam.  ; 
phenol-phthalein  solution  ;  Na. 


Fig.  148 


SODIUM  351 

4.  Color  change  of  sodium  peroxide  by  heat.  —  One  gram 
of  sodium  peroxide  is  heated  in  a  test-tube.  The  powder 
undergoes  a  marked  change  in  color  from  white  to  yellow. 
This  change  in  color,  however,  indicates  no  chemical  change, 
as  the  introduction  of  a  glowing  splinter  fails  to  detect  any 
evolution  of  oxygen,  and,  on  cooling,  the  yellow  disappears. 

Sodium  peroxide ;  splinter. 

5.  Oxidizing  action  of  sodium  peroxide.  —  (a)  With  phos- 
phorus.  —  A  very  small  quantity  of  sodium  peroxide  is  care- 
fully mixed  on  paper  with  an  equal  volume  of  red  phosphorus. 
The  mixture  is  then  wrapped  in  a  powder  paper  (Ex.  25,  p. 
248),  placed  on  an  anvil,  and  struck  with  a  hammer.  A 
sharp  report  is  heard.     (Gauntlets.) 

Hammer  and  anvil ;  powder  paper  (Ex.  25,  p.  248)  ;  gauntlets  ; 
NasOa ;  red  P. 

(h)  With  carbon.  —  A  small  quantity  of  powdered  char- 
coal is  minted  with  an  equal  volume  of  powdered  sodium 
peroxide  and  gently  heated.    The  oxidation  is  very  vigorous. 

The  sodium  peroxide  should  first  be  placed  in  the  test- 
tube  and  then  the  charcoal  added  and  the  mixture  well 
shaken.  At  times  the  reaction  will  take  place  even  in  the 
cold. 

The  mixture  of  charcoal  and  sodium  peroxide  may  be 
caused  to  explode  by  adding  one  drop  of  water.  The  exper- 
iment should  be  performed  behind  a  glass  screen. 

A  few  drops  of  nitrobenzene  are  allowed  to  fall  upon  1  or 
2  g.  of  powdered  sodium  peroxide  in  a  dry  test-tube.  On 
gently  heating  the  tube  an  explosion  is  obtained. 

Glass  screens  ;  Na202 ;  nitrobenzene  ;  powdered  charcoal. 

6.  Supersaturation   of  sodium    sulphate   solution.  —  The 

phenomenon  attending  the  disturbance  of  a  supersaturated 
solution  is  well  shown  by  the  solution  of  sodium  sulphate. 


352  CHEMICAL  LECTURE  EXPERIMENTS 

Two  hundred  grams  of  crystallized  sodium  sulphate  are 
heated  in  a  500  cc.  flask  until  the  salt  has  completely  melted. 
A  plug  of  cotton  should  then  be  placed  in  the  mouth,  and 
the  flask  allowed  to  stand  until  cold.  If  the  operation  is 
performed  with  care,  the  salt  will  remain  in  the  liquid  con- 
dition. On  removing  the  cotton  plug,  and  dropping  a  small 
crystal  of  sodium  sulphate  into  the  melted  liquid,  the  con- 
tents of  the  flask  immediately  solidify. 

If  the  bulb  of  the  ether  thermometer  (Ex.  73,  p.  174)  is 
inserted  in  the  liquid,  the  rise  in  temperature  resulting  from 
the  solidification  of  the  salt  will  cause  the  ether  to  boil  and 
escape  from  the  mouth  of  the  tube. 

The  solidification  of  the  supersaturated  solution  may  also 
be  accomplished  by  rapidly  pouring  it  into  a  crystallizing 
dish. 

By  agitating  it  with  a  glass  rod,  the  liquid  may  be  caused 
to  solidify  while  in  the  flask. 

500  cc.  flask  ;  cotton-batting  ;  ether  thermometer  (Ex.  73,  p.  174)  ; 
crystallized  Na2S04. 

7.  Freezing  mixture  of  sodium  sulphate  and  hydrochloric 
acid.  —  Crystallized  sodium  sulphate,  when  mixed  with 
hydrochloric  acid,  produces  a  lowering  in  temperature 
amounting  to  nearly  30°  C. 

Eighty  grams  of  the  crystallized  salt  are  finely  pulverized 
and  mixed  in  a  flask  with  40  cc.  of  concentrated  hydro- 
chloric, acid.  If  the  flask  is  placed  upon  a  few  drops  of 
water  on  a  block,  the  water  will  be  frozen  and  the  flask 
cemented  to  the  wood.  The  acid  must  be  previously  cooled 
to  10°  C. 

Flask  ;  block  of  wood  ;  NaaSOi  +  lOHgO  ;  con.  HCl. 

8.  Formation  of  metallic  silicates  in  a  solution  of  sodium 
silicate.  —  The  metallic  silicates  may  be  formed  in  a  solution 


SODIUM 


353 


of  sodium  silicate  by  dropping  crystals  of  the  various  salts 
into  the  liquid.  As  the  silicate  forms  it  spreads  out  in  a 
treelike  structure. 

A  liter  beaker  is  filled  with  a  solu- 
tion of  sodium  silicate  having  a  specific 
gravity  of  1.10.  Crystals  of  cobalt  ni- 
trate, nickel  sulphate,  uranium  nitrate, 
manganese  sulphate,  ferrous  sulphate, 
and  copper  sulphate  are  allowed  to  fall 
in  the  beaker  and  rest  on  different  parts 
of  the  bottom  (Fig.  149).  The  forma- 
tion of  the  silicates  requires  some  time, 
though  frequently  marked  indications  of 
their  formation  may  be  observed  at  the  end  of  half  an  hour. 
The  beaker  should  be  placed  in  a  quiet  place,  and  not  dis- 
turbed until  the  next  exercise. 

Large  beaker;    water-glass  solution   (sp.   gr.    1.10);    crystals  of 
Co(N03)2,  NiSOi,  Ur02(N03)2,  MnS04,  FeSOi,  CUSO4. 


Fig.  149 


2a 


POTASSIUM 


1.  Vaporization.  —  Potassium,  when  strongly  heated  in  a 
glass  test-tube,  yields  a  green  vapor. 

A  small  piece  of  potassium,  carefully  cleaned  and  dried, 
is  placed  in  a  dry  test-tube  and  strongly  heated.  The  metal 
is  vaporized  and  rapidly  attacks  the  glass,  liberating  the 
silicon.     The  interior  of  the  tube  becomes  blackened. 

The  color  of  the  potassium  vapor  may  be  better  seen  if  a 
piece  of  clean,  dry  potassium  is  heated  in  a  bulb-tube  through 
which  a  current  of  dry  hydrogen  is  passed.  After  making 
sure  that  the  bulb  is  filled  with  hydrogen  and  that  all  air  is 
expelled,  the  potassium  is  strongly  heated  in  a  blast-lamp, 
the  supply  of  hydrogen  being  cut  down  to  a  minimum. 
If  the  heat  is  supplied  quickly,  the  globule  of  molten  potas- 
sium bursts,  filling  the  whole  bulb  with  a  green  vapor. 

The  current  of  hydrogen  may  be  increased,  and  the  issuing 
gas  will  burn  with  the  violet  flame  of  potassium. 

H  generator  ;  dry  test-tube  ;  dry  bulb-tube  ;  blast-lamp ;  K. 

2.  Union  of  potassium  and  bromine.  —  Potassium  and 
bromine  unite  with  explosive  violence  to  form  potassium 
bromide. 

A  3  mm.  piece  of  potassi,um  is  carefully  dried  between 
filter-paper  and  dropped  into  a  test-tube  containing  a  few 
drops  of  bromine.  As  the  reaction  is  so  violent,  special 
precautions  are  necessary  when  performing  this  experiment. 

354 


POTASSIUM  355 

The  test-tube  must  be  placed  inside  a  wide-mouthed  bottle 
(Fig.  109,  p.  262)  to  collect  the  bromine  in  case  of  accident. 
The  closed  end  of  the  test-tube  is  thrust  through  a  hole  in  a 
cork  or  piece  of  cardboard.  A  large  inverted  funnel,  with  a 
cork  in  the  stem,  is  suspended  by  a  ring-stand  15  cm.  directly 
above  the  tube,  to  prevent  pieces  of  pota^ssium  or  drops  of 
bromine  from  coming  out  of  the  tube.  Finally,  the  hands 
should  always  be  protected  with  gauntlets. 

2  K  -f  Br2  =  2  KBr. 

Apparatus  (Fig.  109,  p.  262)  ;  wide-mouthed  bottle  ;  cardboard  ; 
funnel ;  gauntlets  ;  K  ;  Br. 

3.  Union  of  potassium  and  iodine.  —  When  heated,  potas- 
sium and  iodine  unite  directly  with  explosive  violence. 

A  3  mm.  piece  of  potassium  is  gently  warmed  in  a  clean, 
dry  test-tube,  with  a  crystal  of  iodine.  The  elements  unite 
with  an  explosion. 

Dry  test-tube  ;  K  ;  I. 

4.  Use  of  potassium  nitrate  in  touch-paper.  —  Unsized 
paper  drenched  in  concentrated  potassium  nitrate  solution 
and  then  dried  finds  much  use  as  touch-paper  for  igniting 
combustible  mixtures.  A  quantity  of  the  paper  should  be 
prepared  for  general  lecture-table  use. 

A  solution  of  potassium  nitrate,  saturated  at  the  tempera- 
ture of  the  room,  is  placed  in  a  small  beaker.  Strips  of 
filter-paper  are  then  thoroughly  moistened  with  the  solution, 
hung  up,  and  allowed  to  dry  (not  by  a  flame).  If  the  solu- 
tion is  saturated  at  the  boiling  temperature,  an  excess  of 
nitre  will  be  crystallized  on  the  surface  of  the  paper  in  such 
a  way  as  to  be  continually  rubbing  off. 

On  igniting  one  end  of  a  strip  of  the  dried  paper  the 
combustion  will  slowly  proceed  till  the  paper  is  completely 


356  CHEMICAL   LECTUKE   EXPERIMENTS 

consumed.      The  fire  cannot  be  extinguished  by  blowing 
on  it. 

By  means  of  a  fine  camel's-hair  brush  a  letter  or  word  is 
written  on  a  sheet  of  unsized  paper  with  a  concentrated 
solution  of  potassium  nitrate.  After  the  paper  has  become 
thoroughly  dry  and  suitably  suspended,  a  match  touched  to 
one  corner  of  the  word  will  cause  a  lively  combustion,  which 
will  follow  the  line  of  the  word  and  ultimately  burn  it  out. 
A  brush  marking  lines  not  over  3  mm.  in  width  should  be 
used,  as  otherwise  there  is  danger  of  the  whole  paper 
taking  fire. 

Unsized  paper ;  fine  camel's-hair  brush ;  saturated  solution  of 
KNO3. 

6.  Preparation  of  gunpowder.  —  Thirty  grams  of  finely 
powdered  potassium  nitrate,  5  g.  of  powdered  charcoal,  and 
5  g.  of  sulphur  flowers  are  intimately  mixed  on  paper. 
Three-fourths  of  this  mixture  is  placed  on  a  plate  or  a  piece 
of  asbestos  paper  and  ignited  in  the  hood.  When  the  mix- 
ture is  ignited,  it  burns  brightly,  leaving  a  residue  which 
contains  potassium  sulphide.  On  moistening  the  residue 
with  hydrochloric  acid,  hydrogen  sulphide  is  liberated. 

The  value  of  pressing  and  granulating  gunpowder  is 
markedly  shown  by  the  following  experiment :  The  remain- 
der of  the  above  mixture  is  placed  on  one  square  of  asbes- 
tos and  an  equal  quantity  of  gunpowder  is  placed  on  a 
second  square.  Two  strips  of  touch-paper  are  cut  of  equal 
length  and  inserted  in  the  two  heaps  of  powder.  After 
placing  the  asbestos  squares  in  the  hood  the  touch-paper 
is  ignited.  The  commercial  gunpowder  burns  with  an 
instantaneous  flash,  while  the  mixture  burns  much  more 
slowly. 

Asbestos  paper ;  touch-paper ;  gunpowder  ;  KNO3 ;  powdered 
charcoal :  S  flowers. 


POTASSIUM  357 

6.  Combustion  of  phosphorus  in  potassium  chlorate. — A 

depression  is  made  in  the  top  of  a  small  heap  of  finely  pul- 
verized potassium  chlorate  on  asbestos  paper.  A  3  mm. 
piece  of  well-dried  phosphorus  is  laid  in  the  depression  and, 
after  placing  the  asbestos  plate  in  a  strong  draft,  the  phos- 
phorus is  ignited  by  means  of  a  candle  or  taper  on  the  end 
of  a  long  stick.  The  phosphorus  burns  fiercely  in  the 
oxygen  liberated  from  the  potassium  chlorate. 

Asbestos  paper  ;  candle  on  long  stick  ;  KCIO3  ;  P. 

7.  Use  of  potassium  chlorate  in  colored  fires  (Bengal  fires). 

—  In  all  mixtures  containing  potassium  chlorate  it  is  of  the 
utmost  importance  that  each  substance  should  be  reduced  to 
a  fine  powder  before  mixing,  and  that  the  mixing  should 
be  done  on  paper  with  the  fingers  (never  in  a  mortar !  !  !), 
causing  as  little  friction  as  possible.  With  reasonable  care 
no  difficulty  will  be  experienced. 

The  ignition  of  colored  fires  is  most  satisfactorily  effected 
by  igniting  a  piece  of  touch-paper  inserted  in  the  top  of  the 
conical  pile  of  powder.  Ignition  from  a  match  is  exceed- 
ingly uncertain  and  at  times  dangerous. 

A  characteristic  fire  may  be  prepared  by  mixing  2  g. 
of  copper  sulphate,  2.5  g.  of  sulphur  flowers,  and  15  g.  of 
potassium  chlorate.  This  mixture,  when  ignited,  burns 
with  a  purple  flame. 

Asbestos  paper  ;  touch-paper  ;  CuSO^  ;  KCIO3  ;  S  flowers. 


AMMONIUM  COMPOUNDS 


1.  Preparation  of  ammonium  amalgam. — This  interest- 
ing amalgam  is  prepared  by  the  action  of  sodium  amalgam 
of  a  soft,  waxy  consistency  on  a  warm  saturated  solution  of 
ammonium  chloride.  The  sodium  amalgam,  when  kneaded 
with  the  fingers  in  the  ammonium  chloride  solution,  which 
it  rapidly  attacks,  swells  up  and  forms  a  butterlike  mass, 
which  is  porous  and  rapidly  decomposes. 

Sodium  amalgam  ;  saturated  NH4CI  solution. 

2.  Preparation  of  ammonium  amalgam  by  the  electrolysis 
of  a  solution  of  ammonium  sulphate. — By  the  electrolysis 

of  ammonium  sulphate  free  ammonium  is 
liberated  at  the  negative  pole,  and  if  an 
electrode  of  mercury  is  used,  the  ammonium 
amalgamates  with  it,  forming  ammonium 
amalgam. 

A  saturated  solution  of  ammonium  sulphate 
is  placed  in  a  150  cc.  cylinder  having  a  2  cm. 
layer  of  mercury  on  the  bottom  (Fig.  150).  A 
well-insulated  copper  wire  is  thrust  into  the 
solution  and  the  bare  end  pressed  under  the 
mercury.  The  positive  electrode  should  con- 
sist of  a  small  piece  of  platinum.  On  pass- 
ing a  current  from  4  cells  of  a  "  bichromate  " 

battery  through  the  solution  the  decomposition  is  effected. 

The  mercury  at  the  bottom  of  the  cylinder  swells  up  with 

358 


Fig.  150 


AMMONIUM  COMPOUNDS 


359 


the  formation  of  ammonium  amalgam,  and  care  should  be 
taken  to  stop  the  current  before  the  mercury  has  reached 
the  platinum  electrode.  A  piece  of  ordinary  annunciator 
wire  which  is  well  covered  with  paraffin  will  serve  as  a 
conductor  to  the  mercury  electrode. 

Battery  ;  150  cc.  cylinder;   annunciator  wire  ;  Pt  electrode  ;  Hg ; 
(NH4)2S04  saturated  solution. 

3.  Union  of  ammonia  and  hydrochloric  acid  to  form  ammo- 
nium chloride.  —  (a)  A  liter  cylinder  is  filled  with  hydro- 
chloric acid  gas  either  by  downward  displacement  or  by 
shaking  5  cc.  of  concentrated  hydrochloric  acid  about  in  it 
for  a  few  minutes,  and  is  then  covered  with  a  glass  plate. 
A  brush  such  as  is  used  for  cleaning  lamp  chimneys  is 
drenched  with  strongest  ammonium  hydroxide,  and  plunged 
suddenly  into  the  jar  of  hydrochloric  acid.  A  piece  of  card- 
board large  enough  to  cover  the  jar  may  be  slipped  over  the 
brush  handle  and  the  brush  suspended  in  the  middle  of  the 
jar,  the  glass  plate  being  quickly  removed  at  the  moment 
of  inserting  the  brush.  The  cardboard  prevents  any  escape 
of  ammonium  chloride  fumes.  As  the 
strongest  ammonium  hydroxide  is  disagree- 
able to  use  in  an  open  room,  it  is  advisable 
to  crowd  the  brush  down  into  a  cylinder  just 
large  enough  to  hold  it  before  pouring  on 
the  ammonium  hydroxide.  A  small  quan- 
tity of  ammonium  hydroxide  will  thereby 
suffice  to  drench  the  brush  thoroughly. 

Brush  ;  cardboard  ;  con.  HCl,  or  HCl  generator  ; 
con.  NH4OH. 


(b)    Two  tubulated  bell-jars,  each  fitted  ^j^  ^^g^ 

with  a  one-holed  rubber  stopper  carrying 
a  short  piece  of  glass  tubing,  are  connected  by  a  piece  of 
rubber  tubing  slipped  over  the  glass  tubes  (Fig.  151).     The 


360  CHEMICAL  LECTURE  EXPERIMENTS 

bell-jars  are  clamped  in  a  vertical  position  and  the  rubber 
tube  closed  with  a  pinch-cock.  The  lower  bell-jar  is  filled 
with  ammonia  by  displacement  and  the  upper  with  hydro- 
chloric acid  gas  by  displacement.  On  opening  the  pinch- 
cock  the  ammonia,  by  reason  of  its  smaller  specific  gravity, 
ascends  through  the  rubber  tube  and  forms  white  clouds  in 
the  upper  bell-jar. 

Two  tubulated  bell-jars  ;  corks  ;  tubes  and  pinch-cock  ;  NHs  sup- 
ply ;  HCI  gas  supply. 

4.  Union  of  ammonia  and  hydrogen  sulphide.  —  Crystal- 
lized anhydrous  ammonium  sulphide  results  from  the  inter- 
action of  dry  ammonia  gas  and  dry  hydrogen  sulphide.         / 

A  clean,  dry,  3  1.  flask  is  filled  with  ammonia  gas 
by  displacement.  When  completely  filled  a  current  of 
hydrogen  sulphide,  dried  by  passing  over  calcium  chloride, 
is  conducted  into  the  flask.  On  cooling  the  flask  somewhat, 
a  deposit  of  fine  crystals  of  ammonium  sulphide  will  appear 
on  the  interior. 

2  NH3  +  H2S  =  (NH4)2S. 

3  1.  flask  ;  NH3  supply  ;  HgS  supply. 

5.  Dissociation   of   ammonium  sulphate    solution.  —  Two 

grams  of  ammonium  sulphate  are  dissolved  in  300  cc.  of 
water  in  a  500  cc.  retort.  Blue  litmus  solution  is  intro- 
duced, one  drop  of  ammonium  hydroxide  being  added,  if 
necessary,  to  give  a  decidedly  alkaline  color.  The  retort  is 
placed  on  a  ring-stand  and  clamped,  with  the  neck  dipping 
into  a  500  cc.  flask  containing  100  cc.  of  litmus  solution 
colored  red  by  the  addition  of  one  drop  of  dilute  sulphuric 
acid.  On  gently  heating  to  the  boiling  point  (care  being 
taken  to  prevent  too  violent  ebullition,  as  otherwise  some 
of  the  fluid  made  alkaline  is  liable  to  be  mechanically  car- 
ried over),  ammonia  gas  distils  over,  and  soon  the  upper 


AMMONIUM   COMPOUNDS  361 

portion  of  the  liquid  in  the  receiver  will  be  seen  to  have 
acquired  a  blue  color,  while  the  liquid  in  the  retort  gradu- 
ally turns  a  decided  red.  The  complete  change  in  color  is 
noticed  after  boiling  for  thirty  minutes. 

500  cc.  retort ;  500  cc.  flask  ;  litmus  solution  ;  2  g.  (NH4)2S04. 

6.  Decomposition  of  ammonium  dichromate  by  heat. — 

Ammonium  dichromate,  when  heated,  undergoes  a  complete 
decomposition,  resulting  in  the  formation  of  nitrogen,  water, 
and  chromium  sesquioxide. 

One  or  two  grams  of  powdered  ammonium  dichromate  are 
heated  in  a  hard-glass  test-tube  till  the  decomposition,  which 
is  characterized  by  an  increase  in  volume  of  the  mass  and 
an  appearance  of  fire,  begins.  The  heat  of  the  decomposi- 
tion, when  once  started,  is  sufficient  for  completion,  and  the 
mass  expands,  filling  the  tube  with  a  tealike  substance, 
chromic  oxide..  Nitrogen  gas  is  given  off,  and  a  lighted 
match  thrust  in  the  tube  is  extinguished.  At  the  end  of 
the  reaction  the  water-vapor  formed  escapes  as  steam  at  the 
mouth  of  the  tube.  The  residue  of  chromic  oxide  formed 
may  be  poured  upon  a  white  plate,  where  its  peculiar  form 
is  more  easily  observed. 

(]SrH4)2Cr20,  =  Cr^Og  -f  4  H^O  +  Nj,. 

Hard-glass  test-tube  ;  white  plate  ;  (NH4)2Cr207. 

7.  Decomposition  of  solid  ammonium  nitrate  by  zinc  dust. 

—  If  ammonium  nitrate  in  the  solid  form  is  mixed  with  zinc 
dust,  the  reduction  is  so  vigorous  as  to  produce  a  great  in- 
crease in  temperature,  which,  under  certain  conditions, 
causes  the  ignition  of  the  zinc. 

A  mixture  of  8  g.  of  ammonium  nitrate  and  1  g.  of  am- 
monium chloride  is  spread  out  in  a  thin  layer  on  an  iron 
plate.  A  layer  of  equal  thickness  of  zinc  dust  is  sprinkled 
on  top  of  this  layer.     On  allowing  one  drop  of  water  to  come 


362  CHEMICAL    LECTURE    EXPERIMENTS 

in  contact  Avith  this  mixture,  the  reaction  takes  place,  and 
the  heat  developed  is  so  great  as  to  cause  an  ignition  of  the 
zinc  dust.  The  ammonium  nitrate  should  be  previously 
dried,  for,  owing  to  its  hygroscopic  nature,  it  will  retain 
enough  moisture  to  cause  a  premature  ignition  of  the  zinc 
without  the  addition  of  water.  In  fact,  the  experiment  may 
be  performed  by  using  a  moist  ammonium  nitrate,  and  the 
addition  of  water  dispensed  with.  Care  should  be  taken, 
however,  to  prevent  any  danger  from  the  premature  igni- 
tion of  the  zinc  dust,  as  it  will  probably  be  ignited  before 
the  mixture  of  the  ammonium  salts  can  be  entirely  covered 
with  it. 

Iron  plate  ;  NH4NO3  ;  NH4CI ;  Zn  dust. 

8.  Preparation  of  ammonium  carbonate  (carbamate  ?  ) 
from  ammonia  and  carbon  dioxide.  —  Dry  carbon  dioxide, 
when  allowed  to  come  in  contact  with  dry  ammonia,  forms 
ammonium  carbamate,  a  constituent  of  commercial  ammo- 
nium carbonate. 

A  dry  3  1.  flask  (Fig.  92,  p.  222)  is  filled  with  ammonia 
by  displacement,  and  a  slow  stream  of  dry  carbon  dioxide  con- 
ducted into  it.  After  a  short  time  the  walls  of  the  flask  become 
covered  with  a  crystalline  deposit  of  ammonium  carbamate. 

3  1.  flask  ;  NH3  supply  ;  CO2  generator. 

9.  Preparation  of  ammonium  carbonate  by  the  inter- 
action of  ammonia  and  carbon  dioxide  in  an  alcoholic  solu- 
tion. —  When  carbon  dioxide  is  conducted  into  an  alcoholic 
solution  of  ammonia,  a  white  crystalline  deposit  of  ammo- 
nium carbonate  (ammonium  carbamate  ?  )  is  formed. 

Fifty  cubic  centimeters  of  alcohol  are  saturated  with  am- 
monia gas  and  a  rapid  stream  of  carbon  dioxide  conducted 
through  the  solution  in  a  beaker. 

Alcohol ;  CO2  generator  ;  NHs  supply.* 


CALCIUM 


1.  Action  of  calcium  oxide  with  water.  —  Calcium  oxide 
unites  with  water,  with  the  liberation  of  great  heat,  to  form 
calcium  hydroxide. 

A  piece  of  freshly  burned  quicklime  is  immersed  in  water 
for  two  or  three  seconds  and  then  placed  on  a  plate.  In  a 
few  moments  the  lime  becomes  very  much  heated,  swells  up, 
and  falls  to  a  powder. 

Four  or  five  lumps  of  quicklime  may  be  placed  in  a  large 
evaporating-dish  and  moistened  with  hot  water.  The  lime 
swells  up,  filling  the  evaporating-dish,  and  giving  rise  to 
intense  heat.  A  match  may  be  ignited  by  placing  the  head 
in  one  of  the  crevices  formed  as  the  lime  crumbles. 

If  an  especially  good  piece  of  lime  is  available,  the  heat 
is  often  sufficient  to  ignite  gunpowder.  The  lime  should 
be  placed  on  a  plate  and  drenched  with  boiling  water.  As 
soon  as  the  reaction  begins,  .5  g.  or  less  of  gunpowder  should 
be  sifted  from  a  piece  of  paper  or  card  upon  the  lime.  Care 
should  be  taken  to  close  the  powder-container  and  remove  it 
from  any  possible  danger  of  accidental  explosion  before  pour- 
ing the  water  upon  the  quicklime. 

Crockery  plates  ;  hot  water  ;  fresh  quicklime  ;  gunpowder. 

2.  Calcium  oxide  as  a  drying  agent.  —  The  affinity  of  cal- 
cium oxide  for  moisture  makes  this  compound  an  effective 
drying  agent  for  many  gases. 

363 


364 


CHEMICAL   LECTURE   EXPERIMENTS 


The  absorption  of  moisture  from  a  gas  by  calcium  oxide 
may  be  shown  by  moistening  the  interior  of  a  bell-jar  by 
holding  it  over  a  hydrogen  flame  and  then  placing  it  on  a 
porcelain  plate  in  the  centre  of  which  are  a  few  lumps  of 
good  quicklime.  A  second  bell-jar  may  advantageously  be 
moistened  and  placed  over  a  plate  containing  no  lime.  In 
a  short  time  all  the  moisture  on  the'  walls  of  the  bell-jar 
covering  the  lime  will  disappear,  while  the  other  jar  will 
remain  unchanged  (Fig.  76,  p.  175). 

Two  1.  bell-jars  ;  2  plates  ;  H  flame  ;  fresh  quicklime. 

3.  Preparation  of  calcium  phosphide.  —  Phosphorus, 
when  in  contact  with  heated  quicklime,  forms  calcium  phos- 
phide. 

Five  grams  of  well-dried  yellow  phosphorus  are  inserted 
in  a  50  cm.  length  of  combustion  tubing,  1.5  cm.  internal 


til—! 


(  )      (  » 


E 


C->fl 


^ 


Fia.  152 


diameter,  closed  at  one  end.  A  plug  of  asbestos  is  then 
introduced  and  a  20  cm.  length  of  the  tube  filled  with  lumps 
of  good  quicklime  (Fig.  152).  The  tube  is  so  placed  over  a 
four-tube  burner  that  the  lime  may  be  strongly  heated  before 
heating  the  phosphorus.  When  the  lime  has  become  hot,  the 
phosphorus  is  brought  to  a  boil  and  the  vapor  passed  over 


CALCIUM  365 

the  heated  lime.  The  phosphorus  end  of  the  tube  should  be 
heated  with  a  Bunsen  burner  held  in  the  hand,  and  a  plate 
of  sand  should  be  placed  beneath  the  boiling  phosphorus. 
As  the  phosphorus  vapor  comes  in  contact  with  the  hot  lime, 
the  lime  glows  and  turns  black,  forming  calcium  phosphide. 
The  decomposition  of  the  product  by  water  is  shown  in 
Exs.  29,  30,  p.  252. 

50  cm.  length  combustion-tubing ;  plate  of  sand ;  4-tube  burner ; 
fresh  quicklime ;  P. 

4.  Hydration  of  anhydrous  calcium  sulphate.  —  When 
anhydrous  calcium  sulphate  (plaster  of  Paris)  is  mixed  with 
water,  the  water  combines  with  the  salt,  forming  a  hard  mass 
which  may  be  used  to  take  impressions. 

A  coin  may  be  placed  in  the  bottom  of  a  small  pill-box 
and  the  box  filled  with  a  thick,  freshly  prepared  paste  of 
plaster  of  Paris  and  water.  On  allowing  the  mixture  to 
stand  for  half  an  hour  it  will  harden.  The  bottom  of  the 
box  can  be  cut  away  and  the  coin  removed,  leaving  an  im- 
pression in  the  plaster. 

The  absorption  of  water  by  plaster  of  Paris  may  be  shown 
by  simply  mixing  the  plaster  and  water  to  a  thick  paste. 
In  a  few  moments  the  mixture  will  have  set  sufEciently  to 
remain  in  the  beaker  when  it  is  inverted. 

Pill-box  ;  plaster  of  Paris. 

5.  Decomposition  of  calcium  carbonate  in  an  atmosphere 
of  air  or  hydrogen. — While  calcium  carbonate  is  not  decom- 
posed in  an  atmosphere  of  carbon  dioxide  (see  Ex.  22,  p.  304), 
it  is  readily  decomposed  when  heated  in  an  atmosphere  of 
hydrogen  or  air.     (Burning  limestone.) 

A  few  lumps  of  calcite  are  placed  in  the  bulb-tube  through 
which  a  current  of  hydrogen  freed  from  carbon  dioxide  is 
being  passed.     The  issuing  gas  is  conducted  through  a  glass 


366  CHEMICAL   LECTURE   EXPERIMENTS 

elbow  dipping  into  a  beaker  of  lime-water.  Until  the  calcite 
is  heated  the  lime-water  remains  clear.  As  soon  as  the  bulb 
is  strongly  heated,  carbon  dioxide  is  evolved  and  is  carried 
by  the  hydrogen  current  into  the  lime-water,  where  it  pro- 
duces a  precipitate. 

On  cooling  and  leaching  out  the  contents  of  the  bulb  with 
water,  they  will  be  found  to  be  strongly  alkaline  on  account 
of  the  formation  and  the  subsequent  hydration  of  the  cal- 
cium oxide. 

The  experiment  may  be  repeated  with  the  same  results  by 
using  air  freed  from  carbon  dioxide  in  place  of  hydrogen. 

CaCOg  =  CaO  +  CO2. 

Bulb-tube  ;  H  generator ;  lime-water ;  calcite. 


%%p. 


K'^>% 


\ 


STKONTIUM   AND   BARIUM  % 


1.  Deflagration   of  strontium   nitrate  on   charcoal.  —  A 

crystal  of  strontium  nitrate,  when  thrown  on  glowing  char- 
coal, deflagrates  vigorously,  giving  rise  to  a  red  flame. 

If  charcoal  powder  is  heated  to  glowing  in  an  iron  saucer 
and  powdered  strontium  nitrate  is  thrown  into  the  dish,  the 
combustion  is  brilliant. 

Iron  dish  ;  charcoal ;  Sr(N03)2. 

2.  Use  of  strontium  nitrate  in  red  fire.  —  Strontium 
nitrate  is  the  essential  coloring  ingredient  in  red  fire. 

A  mixture  of  1  g.  of  potassium  chlorate,  11  g.  of  stron- 
tium nitrate,  4  g.  of  sulphur  flowers,  and  .5  g.  of  lamp-black, 
all  of  which  have  been  previously  finely  powdered  and  care- 
fully mixed  on  paper,  burns  with  an  intense  red  flame. 
The  mixture,  which  should  be  placed  in  the  hood,  is  ignited 
with  a  short  piece  of  touch-paper. 

Asbestos  paper  ;  Sr(N03)2  ;  KCIO3 ;  S  flowers  ;  lamp-black  ;  touch- 
paper. 

3.  Preparation  of  barium  peroxide.  —  When  barium  oxide 
is  heated  in  the  presence  of  oxygen,  it  absorbs  oxygen,  form- 
ing barium  peroxide. 

A  20  cm.  length  of  combustion-tubing  provided  with  a 
one-holed  rubber  stopper  at  each  end  is  three-fourths  filled 
with  barium  oxide  and  so  supported  that  it  can  be  heated 
with  a  four-tube  burner  (Fig.  153).     A  current  of  oxygen, 

367 


368 


CHEMICAL   LECTURE   EXPERIMENTS 


which  is  allowed  to  bubble  through  sulphuric  acid  in  a  gas 
washing-bottle,  is  passed  through  the  tube,  the  issuing  gas 
bubbling  through  a  second  gas  washing-bottle  at  the  other 


Fig.  153 

end.  On  heating  the  barium  oxide  oxygen  will  be  absorbed 
and  the  rate  of  bubbling  in  the  second  bottle  will  be  much 
less  than  that  in  the  first. 

The  barium  oxide  should  not  be  heated  too  much,  as  other- 
wise the  oxygen  will  again  be  expelled. 

2  BaO  4-  O2  =  2  BaOg. 

Two  gas  washing-bottles  ;  20  cm.  length  combustion-tubing ;  4-tube 
burner ;  0  supply  ;  BaO. 

4.  Decomposition  of  barium  peroxide  by  heat.  —  A  por- 
tion of  the  barium  peroxide  from  the  preceding  experiment 
may  be  heated  in  a  test-tube  and  the  liberated  oxygen  tested 
with  a  glowing  splinter. 

Hydrated  barium  peroxide  on  heating  yields  large  quanti- 
ties of  water,  which  are  likely  to  condense  and  break  the 
tube.  If,  however,  it  is  carefully  heated  until  no  more 
steam  escapes,  the  temperature  may  be  raised  and  the 
oxygen  liberated.  The  residue  on  treatment  with  water 
yields  an  alkaline  solution  of  barium  hydroxide. 

5.  Action  of  hydrogen  on  barium  peroxide. — When  barium 
peroxide  is  heated  in  an  atmosphere  of  hydrogen,  the  reac- 


STRONTIUM    AND    BARIUM  369 

tion  is  very  vigorous,  the  barium  peroxide  becoming  heated 
to  incandescence. 

A  small  quantity  of  barium  peroxide  is  placed  in  a  bulb- 
tube  through  which  a  current  of  hydrogen  is  being  passed. 
On  heating  the  barium  peroxide  slight  explosions  of  oxy- 
hydrogen  gas  take  place  in  the  bulb,  the  barium  peroxide 
appearing  brilliantly  incandescent. 

Bulb-tube  ;  H  generator  ;  Ba02. 

6.  Barium  sulphate  from  barium  oxide  and  sulphur  tri- 
oxide.  —  Sulphur  trioxide  unites  directly  with  barium  oxide 
to  form  barium  sulphate.  The  evolution  of  heat  in  the 
operation  is  great  and  consequently  the  sulphur  trioxide 
(or  fuming  sulphuric  acid)  should  be  placed  in  a  test-tube 
clamped  over  a  dish  of  sand.  On  carefully  sifting  a  small 
quantity  of  barium  oxide  into  2  g.  of  the  sulphur  trioxide, 
the  reaction  takes  place  accompanied  by  lighto 

BaO  -f  SO3  =  BaSO^. 

Plate  of  sand  ;  SO3  or  fuming  H2SO4 ;  BaO. 

7.  Insolubility  of  barium  sulphate  in  water.  —  The  great 
insolubility  of  barium  sulphate  in  water  may  be  interest- 
ingly shown  by  adding  sulphuric  acid  to  successive  quan- 
tities of  increasingly  diluted  solutions  of  barium  chloride. 
Fifty  cubic  centimeters  of  a  saturated  solution  of  barium 
chloride  are  placed  in  a  100  cc.  cylinder.  Five  cubic  centi- 
meters of  this  solution  are  placed  in  a  second  100  cc.  cylinder 
and  sufficient  water  added  to  dilute  the  solution  to  50  cc. 
Five  .cubic  centimeters  of  this  dilute  solution  are  placed  in 
a  third  cylinder  and  diluted  to  50  cc,  the  operation  being 
carried  out  to  the  fifth  dilution.  On  adding  equal  quan- 
tities of  dilute  sulphuric  acid  to  each  of  the  cylinders 
various  degrees  of  turbidity  will  be  obtained,  the  fifth  cylin- 

2b 


370  CHEMICAL   LECTURE  EXPERIMENTS 

der  containing,  however,  a  distinct  precipitate  of  barium 
sulphate. 

This  experiment  may  be  reversed  by  using  concentrated 
sulphuric  acid  and  diluting,  adding  a  solution  of  barium 
chloride  as  the  reagent. 

BaCla  4-  H2SO4  =  BaS04  +  2  HCl. 
Five  100  cc.  cylinders  ;  BaCl2  solution. 

8.  Deflagration  of  barium  nitrate  and  chlorate  on  char- 
coal. —  A  piece  of  charcoal  having  a  small  hollow  scooped 
out  on  one  side  is  heated  to  glowing  in  the  Bunsen  flame.  On 
throwing  a  few  crystals  of  barium  nitrate  on  the  charcoal 
the  salt  deflagrates  vigorously. 

If  barium  chlorate  instead  of  barium  nitrate  is  used,  a 
most  violent  combustion  takes  place. 
Charcoal ;  Ba(N03)2  ;  Ba(C103)2. 

9.  Use  of  barium  nitrate  in  green  fire.  —  Barium  nitrate 
is  the  essential  coloring  ingredient  in  green  fire. 

A  mixture  of  3  g.  of  finely  powdered  potassium  chlorate, 
8  g.  of  finely  powdered  barium  nitrate,  and  3  g.  of  sulphur 
flowers,  when  intimately  mixed  and  ignited  on  asbestos 
paper,  burns  with  an  intense  green  flame. 

Asbestos  paper ;  touch-paper  ;  KCIO3  ;  Ba(N03)2  ;  S  flowers. 

10.  Deflagration  of  barium  chlorate.  —  Barium  chlorate, 
when  heated  on  a  platinum  wire  in  a  Bunsen  burner,  defla- 
grates, imparting  an  intense  green  color  to  the  Bunsen  flame. 

The  deflagration  may  be  carried  out  on  a  much  larger  scale 
by  directing  the  Bunsen  burner  on  a  small  heap  of  barium 
chlorate  on  asbestos  paper. 

When  thrown  on  hot  charcoal,  the  salt  deflagrates  vigor- 
ously. 

Asbestos  paper  ;  Pt  wire  ;  Ba(  0103)2. 


MAGNESIUM 


1.  Combustion  in  water  vapor.  —  The  decomposition  of 
water  by  magnesium,  even  when  in  a  finely  divided  state,  is 
at  best  very  slow,  and  the  hydrogen  is  liberated  in  such  a 
manner  as  to  prevent  its  collection. 

At  a  high  temperature,  however,  the  reaction  between 
magnesium  and  water  vapor  is  intense,  large  quantities  of 
hydrogen  being  liberated. 

Three  hundred  cubic  centimeters 
of  distilled  water  are  vigorously 
boiled  in  a  Jena  glass  Erlenmeyer 
liter  flask  with  a  wide  neck,  and  a 
lighted  taper  is  introduced  into  the 
neck  of  the  flask  to  demonstrate  that 
water  vapor  is  a  non-supporter  of  the 
combustion  of  wood  and  to  indicate 
that  all  the  air  is  driven  out  of  the 
flask.  A  small  quantity  of  magne- 
sium powder  is  ignited  with  a  match 
on  a  deflagrating-spoon  designed  to 
be  turned  over  and  thus  spill  its  con- 
tents (Fig.  154).  A  crude,  though 
thoroughly  practical  and  satisfactory 

spoon  may  be  made  by  fastening  to  a  stout  iron  wire  about 
30  cm.  long  a  round  piece  of  cork,  1  cm.  thick  and  2.5  cm. 
in  diameter,  on  which  rests  a  small  porcelain  crucible  cover, 

371 


Fig.  154 


3T2  CHEMICAL   LECTURE  EXPERIMENTS 

whose  ring  is  pressed  into  a  small  slit  in  the  cork  thus 
making  it  secure.  The  iron  wire  is  thrust  into  the  edge  of 
the  cork  and  bent  upright  close  to  it  to  permit  of  lowering 
the  spoon  into  the  flask.  A  piece  of  string  30  cm.  long  is 
fastened  to  a  tack  or  pin  in  the  rim  of  the  cork  90°  from 
the  point  where  the  iron  wire  is  inserted.  By  pulling  this 
string,  if  the  cork  is  not  fastened  too  tightly  to  the  iron 
wire,  the  spoon  may  be  turned  through  an  angle  of  90°  and 
its  contents. spilled  out. 

After  ignition  in  the  air  the  magnesium  powder  is  lowered 
one-third  of  the  way  into  the  flask  and  the  string  pulled, 
thereby  allowing  the  powder  to  fall  through  the  steam.  A 
blinding  flash  equalled  only  by  the  burning  of  the  powder 
in  air  follows. 

If  the  string  catches  fire  in  the  air,  it  is  instantly  extin- 
guished on  lowering  the  spoon  into  the  flask. 

Inasmuch  as  the  combustion  is  very  rapid  it  is  necessary 
to  cover  the  hand  holding  the  spoon  with  a  gauntlet. 

Mg  -j-  H2O  =  MgO  -f  H2. 

Apparatus  (Fig.  154)  ;  1  1.  Jena  glass  Erlenmeyer  flask  ;  defla- 
grating-spoon  of  special  construction  ;  gauntlets  ;  Mg  powder. 

2.  Combustion  of  magnesium  in  carbon  dioxide.  —  A  300  cc. 

cylinder  containing  a  layer  of  sand  and  a  carbon  dioxide 
delivery-tube  extending  to  the  bottom  is  filled  with  carbon 
dioxide  and  the  dry  gas  allowed  to  flow  continuously  into  it. 
Twenty-five  hundredths  of  a  gram  of  finely  powdered  mag- 
nesium (the  finer  the  powder,  the  better)  is  placed  on  a  2  cm. 
disk  of  previously  ignited  asbestos  paper,  which  can  be 
easily  cut  out  of  sheet  asbestos  by  means  of  a  large-sized 
cork  borer.  The  asbestos  disk  and  the  magnesium  powder 
are  laid  on  a  loop  in  a  stout  iron  wire  thereby  forming  a 
deflagrating-spoon.     On  igniting   the   powder  and  quickly 


MAGNESIUM  373 

lowering  it  into  the  jar  till  the  spoon  touches  the  sand  a 
marked  increase  in  the  intensity  of  the  combustion  takes 
place.  A  piece  of  asbestos  cardboard  with  a  slit  in  it  wide 
enough  to  hold  the  glass  tube  is  quickly  slipped  over  the  top 
of  the  jar.  In  this  way  air  currents  formed  by  the  combus- 
tion of  the  magnesium  will  be  prevented,  and  thus  no  con- 
siderable amount  of  air  admitted.  The  glass  tube  through 
which  the  carbon  dioxide  is  passing  is  now  held  directly 
over  the  burning  magnesium,  and  a  lighted  match  inserted 
in  the  slit  of  the  asbestos.  If  there  is  a  sufficient  supply  of 
carbon  dioxide,  the  match  should  be  extinguished. 

After  the  glow  has  died  out  the  spoon  is  withdrawn  and 
the  rather  compact  mass  of  magnesium  oxide  and  carbon  is 
transferred  by  means  of  a  spatula  from  the  asbestos  disk  to 
a  white  plate.  While  the  exterior  of  the  mass  appears  white 
from  the  coating  of  magnesium  oxide,  on  cutting  the  lump 
in  two  the  interior  will  be  seen  to  be  perfectly  black,  the 
carbon  completely  covering  the  color  of  the  magnesium 
oxide. 

300  cc.  cylinder ;  asbestos  deflagrating-spoon ;  white  plate ;  dry 
CO2  supply. 

3.  Magnesium  and  nitric  acid. — Metallic  magnesium 
reacts  with  nitric  acid,  forming  magnesium  nitrate  with 
the  liberation  of  heat  and  light. 

Five  cubic  centimeters  of  fuming  nitric  acid  are  gently 
warmed  in  a  wide-mouthed  flask.  On  removing  the  lamp 
and  dropping  .25  g.  of  fine  magnesium  powder  on  the  hot 
acid,  the  metal  takes  fire,  burning  with  almost  explosive 
violence.     (Use  gauntlets  and  glass  shields.) 

The  great  quantity  of  oxides  of  nitrogen  evolved  make  it 
necessary  as  a  rule  to  perform  this  experiment  in  a  hood  or 
draft.  In  case  the  first  lot  of  powder  does  not  catch  fire,  a 
like  quantity  must  immediately  be  poured  into  the  neck  of 


374  CHEMICAL   LECTURE   EXPERIMENTS 

the  flask,  gently  tapping  the  paper  in  order  not  to  drop  the 
whole  at  once. 

Gauntlets  ;  shields  ;  Mg  powder  ;  wide-mouthed  100  cc.  flask  ;  fum- 
ing HNO3. 

4.  Reduction  of  metallic  oxides  and  salts.  —  Magnesium  is 
a  very  powerful  reducing  agent  and  will  abstract  the  oxygen 
from  many  metallic  oxides  with  explosive  violence. 

(a)  Magnesium  and  silver  oxide.  —  Equal  volumes  of  mag- 
nesium powder  and  dry  silver  oxide  are  mixed  on  a  paper 
and  a  centimeter  layer  poured  into  a  small,  dry  test-tube. 
The  tube  is  clamped  to  a  retort-stand  in  such  a  position  that 
a  Bunsen  flame  may  be  set  under  it  and  the  bottom  of  the 
tube  come  in  the  hottest  part  of  the  flame.  The  retort-stand 
is  now  placed  between  glass  shields,  and  the  lamp,  resting 
on  a  plate  tilled  with  sand  or  on  a  piece  of  asbestos  paper, 
is  placed  under  the  tube.  (Gauntlets.)  After  a  moment's 
heating,  the  reduction  of  the  silver  oxide  takes  place  with  an 
explosion.  Should  the  tube  be  intact,  the  black  metallic 
silver  will  be  seen  as  a  fine  coating  on  the  sides. 

(&)  Magnesium  and  lithium  carbonate.  —  Lithium  carbon- 
ate is  energetically  reduced  by  magnesium  powder  when  the 
two  are  heated  in  equal  volumes  as  described  above. 

At  the  moment  that  the  reaction  takes  place,  the  fine  red 
color  of  the  burning  lithium  vapor  is  apparent. 

Ag^O  +  Mg  =  MgO  +  2  Ag. 

LigCOg  +  Mg  =  MgO  4-  CO2  4-  2  Li. 

Glass  shields  ;  gauntlets  ;  Ag20  ;  Li.2C03  ;  Mg  powder. 

5.  Combustion  of  magnesium  with  potassium  chlorate.  —  A 

mixture  of  equal  parts  by  volume  of  finely  pulverized  dry 
potassium  chlorate  and  magnesium  powder,  when  ignited 
on  an  asbestos  plate,  gives  an  instantaneous  flash  of  blind- 


MAGNESIUM  375 

ing  intensity.  A  long  taper  or  a  touch-paper  fuse  should 
be  used  in  igniting  the  mixture.  Care  should  be  taken  to 
protect  the  face,  owing  to  the  great  volume  of  smoke  given 
off.  The  above  mixture  is  commonly  used  in  many  of  the 
so-called  flashlight  cartridges. 

Asbestos  paper  ;  touch-paper  ;  gauntlets  ;  colored  glasses  ;  powdered 
KCIO3;  Mg  powder. 

6.  Formation  of  magnesium  nitride.  —  At  a  high  tempera- 
ture magnesium  combines  with  free  nitrogen  to  form  the 
nitride.  The  conditions  for  the  formation  of  the  maximum 
quantity  of  this  compound  are  best  secured  when  1  g.  of 
magnesium  powder  is  heated  in  a  porcelain  crucible  with  a 
Bunsen  burner.  The  crucible  should  not  be  more  than  half 
full  of  the  powdered  metal.  The  powder  soon  begins  to 
burn  on  the  surface,  the  product  being  chiefly  magnesium 
oxide.  The  burning  mass  is  gently  stirred  with  an  iron 
wire,  and  the  combustion  will  slowly  proceed  for  a  few 
minutes.  Under  these  conditions  the  oxygen  is  quickly 
removed  from  the  air,  and  at  the  temperature  of  the  com- 
bustion nitrogen  is  readily  absorbed.  The  resulting  product 
is  a  yellowish  powder  consisting  of  white  magnesium  oxide, 
with  a  varying  proportion  of  magnesium  nitride.  This 
operation  shows  the  method  of  separating  atmospheric  nitro- 
gen from  argon.  The  cooled  product  should  be  securely 
sealed  in  a  bottle. 

3Mg-|-N,  =  Mg3N2. 
Porcelain  crucible  ;  Mg  powder  ;  iron  wire. 

7.  Decomposition  of  magnesium  nitride  by  water.  —  Mag- 
nesium nitride  is  decomposed  by  water,  forming  magnesium 
oxide  and  ammonia. 

A  few  drops  of  water  are  allowed  to  fall  on  some  of 


376  CHEMICAL  LECTURE  EXPERIMENTS 

the  nitride  in  a  test-tube.     A  brisk  evolution  of  a  gas  is 
obtained,  which,  when  tested,  is  seen  to  be  ammonia. 

MggN^  +  3  H2O  =  3  MgO  +  2  NH3. 

8.  Action  of  hydrogen  on  magnesium  nitride.  —  A  current 
of  dry  hydrogen  is  passed  through  a  bulb-tube  containing 
a  small  quantity  of  magnesium  nitride.  On  heating,  am- 
monia will  be  formed  and  may  be  tested  at  the  open  end  of 
the  bulb-tube. 

Bulb-tube  ;  H  generator  ;  Mg8N2. 


ZINC   AND   CADMIUM 


1.  Granulated  zinc.  —  When  melted  zinc  is  poured  in  a 
thin  stream  from  a  height  of  2  or  3  m.  into  a  pail  of  cold 
water,  the  drops  of  melted  metal 
spread  out  on  striking  the  water, 
producing  a  form  of  zinc  called 
granulated  zinc.  The  zinc  should 
have  been  previously  melted  in  a 
large  Hessian  crucible,  which  is 
then  brought  into  the  lecture  room. 

Instead  of  melting  a  large  quan- 
tity of  zinc  before  the  lecture,  the 
apparatus  shown  in  Fig.  155  may 
be  used  to  melt  and  granulate  the 
zinc.  A  Hessian  crucible,  provided 
with  a  3  or  4  mm.  hole  in  the  bot- 
tom, is  strongly  heated  with  a  blast- 
lamp.  Small  lumps  of  zinc  are 
added  from  time  to  time,  and  a  pail 
of  water  is  placed  beneath  the  cru-  p^.^  155 

cible.     As  the  zinc  melts,  it  flows 

out  of  the  opening  in  the  bottom  of  the  crucible  and  drops 
into  the  water  below. 

Hessian  crucible  ;  ditto  with  3  mm.  hole  in  the  bottom ;  blast-lamp  ; 
tongs ;  pail  of  water  ;  Zn. 

377 


-^ 

• 

0 

] 

^ 

1 

\    H-- 


378  CHEMICAL   LECTURE   EXPERIMENTS 

2.  Deposition  of  zinc  on  iron  (galvanized  iron).  —  Iron 
that  is  freed  from  all  oxide,  when  heated  and  dipped  into 
melted  zinc,  becomes  covered  with  a  firmly  adhering  coating 
of  the  metal. 

A  Hessian  crucible  is  filled  with  zinc,  which  is  then 
melted.  A  large  "  cut  "  iron  nail  is  strongly  heated  in  the 
blast,  and  then,  after  cooling,  carefully  cleaned  with  hydro- 
chloric acid  and  sand.  After  washing  off  all  acid  and  dirt, 
the  nail  is  again  heated,  dipped  into  a  little  olive  or  cotton- 
seed oil,  and  then  plunged  into  the  molten  zinc.  On  remov- 
ing and  cooling  the  nail,  it  will  be  found  that  that  portion 
dipped  into  the  zinc  will  have  become  "  galvanized." 

Hessian  crucible  ;  tongs  ;  cut  nail ;  Zn  ;  olive  or  cotton-seed  oil. 

3.  Combustion  of  zinc   dust  and  potassium  chlorate. — 

Ten  grams  of  zinc  dust  are  mixed  with  5  g.  of  finely 
powdered  potassium  chlorate  on  asbestos  paper  The  mix- 
ture, when  ignited,  burns  with  a  white  flame,  leaving  a  yel- 
low residue  of  zinc  oxide,  which,  when  cold,  becomes  white. 

Asbestos  paper  ;  Zn  dust ;  KCIO3. 

4.  Zinc  sulphide  from  zinc  dust  and  sulphur  flowers.  — 

A  mixture  of  zinc  dust  and  sulphur  flowers  burns  with 
great  brilliancy,  forming  zinc  sulphide. 

Ten  grams  of  zinc  dust  and  5  g.  of  sulphur  flowers 
(molecular  amounts)  are  carefully  mixed  on  paper  to  pre- 
vent friction  and  then  lighted  on  a  piece  of  previously 
ignited  asbestos  paper  under  the  hood.  A  brilliant  green- 
ish flame  is  observed.  The  zinc  sulphide  is  intensely 
yellow  while  hot,  but  bleaches  out  to  a  considerable  extent 
on  cooling. 

Zn  +  S  =  ZnS. 

Asbestos  paper ;  Zn  dust ;  S  flowers. 


ZINC    AND    CADMIUM  379 

5.  Distillation  of  cadmium.  —  Cadmium  boils  at  770°, 
and,  when  heated  in  a  bulb-tube  through  which  a  current  of 
hydrogen  is  being  passed,  the  metal  vaporizes  and  condenses 
as  a  metallic  sublimate  in  the  cooler  portions  of  the  tube. 

A  4  or  5  mm.  piece  of  metallic  cadmium  is  placed  in  one 
arm  of  a  bulb-tube  equidistant  between  the  bulb  and  the 
end  of  the  arm.  A  current  of  hydrogen  is  then  passed 
through  the  bulb,  and,  after  all  air  has  been  expelled,  the 
cadmium  is  heated  until  it  boils.  The  interior  of  the  bulb 
becomes  covered  with  a  metallic  deposit. 

Bulb-tube  ;  H  generator  ;  Cd. 

6.  Combustion  of  cadmium  in  air.  —  Cadmium,  at  a  red 
heat,  is  easily  oxidized  in  the  air. 

One  gram  of  cadmium  is  heated  in  a  small  porcelain  cru- 
cible by  means  of  a  good  strong  Bunsen  flame.  The  metal 
melts  and  soon  begins  to  boil.  The  vapor  ignites  and  gives 
rise  to  dense  clouds  of  the  brown  oxide.  On  removing  the 
lamp  suddenly,  the  vapor  can  be  seen  burning  in  the  cru- 
cible, though  after  a  few  seconds  the  flame  goes  out.  The 
inside  of  the  crucible  will  be  covered  with  brown  cadmium 
oxide. 

A  small  piece  of  cadmium  is  placed  in  a  hollow  scooped 
out  of  a  piece  of  charcoal.  By  directing  the  mouth  of  the 
blowpipe,  or,  better  still,  the  blast-lamp,  or  oxy hydrogen  jet 
upon  it,  the  metal  burns  with  more  or  less  vividness  accord- 
ing to  the  source  of  heat.  A  brown  smoke  of  cadmium 
oxide  rises  from  the  burning  globule. 

2  Cd  4-  O2  =  2  CdO. 
Porcelain  crucible  ;  blowpipe  and  charcoal ;  Cd. 

7.  Preparation  of  cadmium  sulphide.  —  When  hydrogen 
sulphide  is  conducted  into  a  cold,  neutral  solution  of  cad- 
mium chloride,  a  yellow  precipitate  of  cadmium  sulphide  is 


380  CHEMICAL   LECTURE   EXPERIMENTS 

obtained.  If,  however,  the  cadmium  solution  is  acidified 
and  kept  hot,  the  sulphide  precipitated  is  of  an  orange-red 
color. 

A  current  of  pure  hydrogen  sulphide  is  conducted  into  a 
series  of  two  gas  washing-bottles,  the  first  of  which  contains 
a  cold,  neutral  solution  of  cadmium  chloride,  the  second  con- 
taining a  hot  solution  of  cadmium  chloride  acidified  with 
hydrochloric  acid.  The  second  gas  washing-bottle  is  placed 
in  a  beaker  containing  hot  water.  On  passing  hydrogen 
sulphide  through  the  system,  cadmium  sulphide  is  precipi- 
tated in  both  bottles  and  is  of  a  yellow  color  in  the  first 
and  of  an  orange-red  in  the  second.  The  solution  in  the 
first  bottle  should  not  contain  an  excessive  amount  of  cad- 
mium chloride,  as  otherwise  considerable  time  will  be 
required  to  saturate  it  with  hydrogen  sulphide. 

Two  gas  washing-bottles  ;  large  beaker  of  hot  water ;  HgS  generator ; 
CdCl2  solution. 


MERCURY 


1.  Purification  and  filtration. — Mercury  may  be  freed 
from  much  foreign  material  by  filtering  through  fine  linen 
or  cambric,  or  through  a  dry,  folded  filter-paper  having  a 
pinhole  in  the  bottom. 

The  chemical  purification  of  mercury  is  effected  by  shak- 
ing the  metal  with  very  dilute  nitric  acid  or  dilute  ferric 
chloride  solution  in  a  large  separating-funnel.  The  purified 
metal  should  be  well  washed  with  water,  the  excess  of  water 
being  removed  by  placing  filter-papers  on  the  surface  of  the 
metal. 

Large  separating-funnel ;  linen  cloth  ;  Hg. 

2.  Iron  amalgam.  — Under  ordinary  conditions  iron  does 
not  amalgamate.  If,  however,  a  piece  of  clean  sheet-iron  is 
rubbed  with  liquid  sodium  amalgam  and  a  filter-paper  wet 
with  saturated  ammonium  chloride  solution,  the  resulting 
ammonium  amalgam  produces  an  amalgamation  of  the  iron. 

Sheet  iron  ;  Na  amalgam  ;  saturated  NH4CI  solution. 

3.  Preparation  of  mercurous  iodide  from  mercury  and 
iodine.  —  Mercury  and  iodine,  when  intimately  rubbed  in 
molecular  proportions,  form  an  amorphous  green  powder 
consisting  of  mercurous  iodide. 

Sixteen  grams  of  mercury  are  placed  in  a  mortar  with 
10  g.  of  iodine.     A  few  drops  of  alcohol  are  then  added, 

381 


382  CHEMICAL   LECTURE   EXPERIMENTS 

and  the  mixture  intimately  rubbed  with  a  pestle.  In  a  few 
moments  a  green  amorphous  powder  will  be  formed.  At 
times  certain  portions  of  the  powder  will  appear  red,  but 
when  all  the  globules  of  mercury  have  disappeared,  the  whole 
mass  will  be  green.  The  compound  should  be  preserved  in 
the  mortar  for  use  in  the  following  experiment. 

2Hg+l2  =  Hgj2. 
Mortar;  Hg ;  L 

4.  Preparation  of  mercuric  iodide  from  mercurous  iodide 
and  iodine.  —  AVhen  mercurous  iodide  is  rubbed  in  a  mortar 
with  an  excess  of  iodine,  it  is  converted  to  mercuric  iodide. 

Ten  grams  of  iodine  are  added  to  the  mercurous  iodide  in 
the  mortar  from  the  preceding  experiment,  and  the  mixture 
thoroughly  rubbed  with  the  pestle.  In  a  short  time  the  green 
mercurous  iodide  will  be  completely  converted  to  the  red 
mercuric  iodide,  all  the  iodine  being  taken  up  in  the  reaction. 

Hg2l2  4-l2  =  2Hgl2. 

Mortar  and  contents  of  preceding  experiment ;  I. 

5.  Formation  of  mercuric  iodide  from  potassium  iodide 
and  mercuric  chloride.  —  A  striking  example  of  a  dry  reac- 
tion is  afforded  by  rubbing  together  equal  weights  of  finely 
powdered  mercuric  chloride  and  finely  powdered  potassium 
iodide  in  a  porcelain  mortar.  The  two  powders,  when  first 
placed  in  the  mortar,  are  perfectly  white,  but  on  intimately 
mixing  them  with  the  pestle  the  mixture  becomes  red  from 
the  formation  of  mercuric  iodide. 

Mortar  and  pestle  ;  finely  powdered  HgCl2  ;  finely  powdered  KI. 

6.  Preparation  of  artificial  cinnabar.  —  A  solution  of  mer- 
curic chloride  is  treated  with  ammonium  hydroxide  as  long 
as  any  precipitate  is  formed.     A  strong  solution  of  sodium 


MERCURY  383 

thiosulphate  is  then  added  to  the  liquid  until  the  precipi- 
tate is  completely  dissolved.  .  If  the  liquid  thus  prepared  is 
heated  for  some  time  in  a  beaker  of  water  at  a  temperature 
of  70°,  a  red  precipitate  of  cinnabar  is  formed. 

If  a  portion  of  the  liquid  is  suddenly  brought  to  a  boil,  the 
cinnabar  is  immediately  precipitated,  but  it  has  a  brownish 
red  color. 

Beaker  of  hot  water  ;  HgCl2  solution  ;  Na2S203  solution. 


COPPER 


1.  Deposition  on  iron.  —  Iron  replaces  copper  in  solutions 
of  cupric  sulphate,  forming  ferrous  sulphate  and  copper. 

A  cleaned  knife-blade  immersed  for  a  few  moments  in  a 
solution  of  cupric  sulphate  becomes  covered  with  a  thin 
coating  of  metallic  copper. 

The  complete  removal  of  copper  from  solutions  may  be 
shown  by  placing  three  or  four  nails  in  a  solution  of  cupric 
sulphate  and  allowing  the  vessel  and  its  contents  to  stand 
twenty-four  hours.  All  the  copper  will  have  been  precipi- 
tated on  the  iron,  the  solution  will  have  lost  its  blue  color, 
and  on  the  addition  of  ammonium  hydroxide  a  greenish 
precipitate  instead  of  a  deep  blue  color  will  be  obtained. 

A  piece  of  zinc  when  immersed  in  cupric  sulphate  solu- 
tion likewise  replaces  the  copper,  and  this  metal  may  be 
used  in  place  of  iron  in  the  above  experiment. 

CUSO4  +  Fe  =  reS04  +  Cu. 
Knife  ;  iron  nails ;  Zn  rod  ;  CUSO4  sol. 

2.  Electrical   deposition   of   copper   (copper   plating).  — 

When  a  current  of  electricity  is  passed  through  a  cupric 
sulphate  solution,  copper  is  deposited  on  one  electrode  while 
oxygen  is  liberated  at  the  other  (Ex.  7,  p.  13). 

Two  platinum  electrodes  are  connected  with  a  bichromate 
battery  and  then  immersed  in  a  solution  of  cupric  sulphate. 

384 


COPPER  385 

Immediately  the  positive  electrode  becomes  covered  with  a 
red  coating  of  copper.  The  negative  electrode  remains 
unchanged.  By  reversing  the  current  the  copper  is  depos- 
ited on  the  clean  electrode  while  the  other  gradually  loses 
its  coating,  ultimately  becoming  perfectly  bright  and  free 
from  copper. 

Cards  with  the  plus  and  minus  signs  should  be  placed 
beside  the  electrodes. 

Bichromate  battery ;  2  Pt  electrodes  ;  -f-  and  —  signs ;  CUSO4  solu- 
tion. 

3.  Color  of  copper.  —  The  color  noticed  on  ordinary  cop- 
per is  partially  due  to  the  presence  of  small  quantities  of  a 
superficial  coating  of  the  oxides  of  copper.  The  true  color 
of  copper  is  shown  by  the  reduction  of  hot  cupric  oxide  by 
alcohol  vapor. 

One  cubic  centimeter  of  ethyl  or  methyl  alcohol  is  poured 
into  a  good-sized  test-tube  loosely  fitted  with  a  rubber 
stopper.  A  copper  spiral  (Ex.  38,  p.  37)  is  then  heated  till 
it  is  thoroughly  oxidized,  and  while  still  hot  carefully  intro- 
duced into  the  test-tube  containing  alcohol.  Immediately 
the  cupric  oxide  coating  on  the  spiral  is  reduced,  and  the 
color  of  metallic  copper  is  seen.  The  rubber  stopper  is 
held  loosely  in  the  test-tube  until  the  expansion  of  the 
gases  in  the  tube  ceases.  At  that  moment  the  cork  is 
firmly  introduced  to  prevent  any  air  from  entering  the  tube. 

After  cooling,  the  cork  is  withdrawn,  and  the  spiral  may 
be  taken  out  and  examined.  This  is  essentially  the  method 
of  preparing  the  reduced  copper  spiral  used  in  elementary 
organic  analysis. 

Copper  spiral  (Ex.  38,  p.  37)  ;  alcohol. 

4.  Action  of  light  on  cuprous  chloride.  —  Sunlight  acts  on 
cuprous  chloride,  changing  its  color  from  white  to  dark  violet. 

2c 


386  CHEMICAL   LECTURE   EXPERIMENTS 

A  quantity  of  the  freshly  precipitated  chloride  may  be 
exposed  to  sunlight  on  a  porcelain  plate. 

On  immersing  a  strip  of  polished  sheet  copper  in  a  con- 
centrated solution  of  cupric  chloride,  the  copper  will  become 
covered  with  a  coating  of  insoluble  cuprous  chloride.  The 
copper  should  then  be  washed  with  running  water,  and  a 
figure  cut  out  of  heavy  paper  placed  over  it.  On  exposure 
to  sunlight  it  will  be  found  that  the  uncovered  portion  of 
the  sheet  will  become  dark  colored,  while  the  covered  por- 
tion will  remain  light. 

Cu  sheet ;  heavy  paper  ;  CUCI2  solution  ;  freshly  precipitated  CU2CI2. 

5.  Flame  coloration  by  cuprous  chloride.  —  The  colora- 
tion of  a  flame  by  cuprous  chloride  may  be  produced  by 

holding  a  piece  of  copper  gauze  in  the  flame 
and  conducting  a  current  of  chlorine  into 
the  opening  at  the  base  of  a  Bunsen  burner 
(Fig.  156).  A  coloration  due  to  the  cuprous 
chloride  is  imparted  to  the  flame. 

The  gauze  should  first  be  strongly  heated 
A       M  and  all  shellac  and  foreign  material  burned 

^^^f^  off.      Chlorine  admitted  at  the  base  of  the 

^    7^        burner,  one  bubble  at  a  time,  produces  in- 
termittent   flashes    of    color    in    the    flame 
which   become  continuous  with   a   steady  introduction  of 
chlorine. 

Cu  gauze ;  small  CI  generator. 

6.  Solubility  of  cupric  chloride  in  alcohol.  —  Cupric 
chloride  dissolves  readily  in  alcohol,  yielding  a  colored 
solution  which  may  advantageously  be  used  to  show  the 
flame  coloration  produced  by  this  salt. 

A  piece  of  previously  ignited  asbestos  paper  is  saturated 


COPPER  387 

with  an  alcoholic  solution  of  cupric  chloride.     On  igniting 
the  alcohol,  a  green  flame  is  obtained. 

Asbestos  paper  previously  ignited  ;  alcohol ;  CuCl2. 

7.  Use  of  cupric  chloride  in  colored  fire.  —  A  mixture  of 
2  g.  of  powdered  charcoal,  2  g.  of  cupric  chloride,  and  4  g. 
of  potassium  chlorate,  ignited  on  asbestos  paper,  yields  a 
blue  flame. 

Asbestos  paper  ;  KCIO3  ;  CUCI2 ;  powdered  charcoal. 


SILVER 


1.  By  electrolysis.  —  (a)  When  an  electric  current  is 
passed  through  a  solution  of  potassium  cyanide  containing 
silver,  the  silver  is  deposited  at  one  pole. 

Sufficient  potassium  cyanide  solution  is  added  to  a  solu- 
tion of  silver  nitrate  to  redissolve  the  precipitate  first 
formed.  The  electrode  connected  with  the  zinc  of  a  bichro- 
mate battery  should  consist  of  a  well-cleaned  and  polished 
strip  of  copper.  The  other  electrode  may  be  a  piece  of 
platinum.  On  passing  a  feeble  current  through  the  solu- 
tion, a  fine  deposit  of  silver  is  formed  on  the  copper. 

Bichromate  battery  ;  Cu  sheet ;  Pt  foil ;  AgNOs  solution ;  KCN 
solution. 

(b)  By  the  electrolysis  of  a  neutral  solution  of  silver 
nitrate  silver  may  be  deposited  in  a  crystalline  form. 

A  concentrated  solution  of  the  salt  is  placed  in  a  beaker, 
and  two  platinum  electrodes,  which  are  connected  with  two 
bichromate  cells,  are  immersed  in  the  liquid.  On  the  nega- 
tive pole  silver  will  be  deposited  in  a  crystalline  mass. 

Bichromate  battery  ;  2  Pt  electrodes  ;  AgNOs  solution. 

2.  Precipitation  by  mercury.  — A  few  grams  of  mercury 
are  placed  in  a  small,  fine-meshed  linen  bag  and  immersed 

388 


SILVER 


389 


beneath  the  surface  of  silver  nitrate  solution  in  a  large 
beaker  (Fig.  157).  In  the  course  of  a  day  or  two  a  fine  net- 
work of  crystallized  silver  will  be  found 
clinging  to  the  bag,  forming  the  so-called 
silver  tree. 

Large  beaker ;  fine-meshed  linen  bag ;  AgNOs  ; 
Hg. 

3.  Formation  of  silver  iodide  in  dilute 
solutions.  —  In  a  solution  containing  a 
mixture  of  a  chloride,  a  bromide,  and 
an  iodide,  to  which  a  solution  of  silver 
nitrate  has    been   added,   the   iodide    is  fig.  157 

always  first  precipitated,  then  the  others. 
To  illustrate  this,  a  saturated  solution  of  sodium  chloride 
is  used,  to  which  5  drops  of  a  solution  containing  2  g. 
of  potassium  iodide  in  50  cc.  of  water  are  added.  This 
gives  a  very  small  amount  of  the  iodide  in  the  pres- 
ence of  a  large  amount  of  the  chloride.  The  addition  of 
3  to  5  drops  of  silver  nitrate  solution,  containing  2.5  g. 
in  50  cc.  of  water,  produces  a  decidedly  yellowish  precipi- 
tate consisting  of  silver  iodide.  On  adding  the  same 
amount  of  silver  nitrate  to  a  saturated  solution  of  sodium 
chloride  free  from  iodide,  the  color  of  the  precipitate  is  a 
pure  white.  In  the  presence  of  a  very  large  excess  of  a 
chloride,  the  small  amount  of  iodide  is  therefore  first  pre- 
cipitated. The  slight  difference  in  color  prevents  the 
demonstration  of  the  analogous  case  of  the  bromide,  for, 
while  the  color  of  silver  iodide  is  markedly  different  from 
the  color  of  the  chloride,  the  same  is  not  true  of  the  differ- 
ences in  color  between  the  bromide  and  the  other  two  com- 
pounds. 


Saturated  NaCl  solution  ;  2  g.  of  KI ;  2.5  g.  of  AgNOs. 


390  CHEMICAL   LECTURE   EXPERIMENTS 

4.  Color  change  of  silver  iodide  on  heating.  —  Silver 
iodide,  when  heated,  changes  its  color,  becoming  intensely 
yellow. 

A  figure  or  character  is  marked  with  a  dilute  solution  of 
silver  nitrate  on  a  card,  which  is  then  dried  out  of  contact 
with  the  light.  The  card  is  then  flowed  with  a  solution  of 
potassium  iodide,  which  converts  the  silver  nitrate  to  silver 
iodide.  After  all  excess  of  potassium  iodide  has  been 
washed  off,  the  card  is  carefully  dried.  On  heating  it 
above  a  Bunsen  flame,  the  character,  which  was  originally 
very  indistinct,  appears  in  bright  yellow  lines.  On  cooling, 
the  color  disappears. 

Card  prepared  with  Agl. 


ALUMINIUM 


1.  Combustion  in  air.  —  Aluminium  wire  or  aluminium 
sheet  does  not  burn  in  the  air.  A  piece  of  wire  held  in  the 
flame  melts  with  superficial  oxidation,  but  does  not  burn. 
Aluminium  sheet  acts  in  a  similar  manner.  Aluminium  fil- 
ings, unless  very  fine,  do  not  readily  burn  by  being  strewn 
through  a  flame.  Aluminium  powder  strewn  through  a 
flame  burns  with  great  brilliancy. 

Aluminium  sheet,  wire,  filings,  leaf,  powder. 

2.  Combustion  in  oxygen.  —  Aluminium  leaf,  when 
strongly  heated  in  a  current  of  oxygen,  burns  brilliantly  to 
form  aluminium  oxide. 

A  bulb-tube  is  filled  with  aluminium  leaf,  and  a  small  bit 
of  string  or  a  shred  of  filter-paper  is  introduced  to  serve  as 
a  kindler.  On  passing  a  current  of  oxygen  through  the 
bulb  and  strongly  heating  the  leaf,  the  string  catches  fire 
and  imparts  the  fiame  to  the  aluminium  leaf,  which  burns  in 
the  atmosphere  of  oxygen  with  a  brilliant  flash. 

4  Al  -h  3  O2  =  2  AI2O3. 

Bulb-tube  ;  string ;  O  supply  ;  Al  leaf. 

3.  Action  of  sodium  amalgam.  —  Mercury  does  not  unite 
readily  with  aluminium  to  form  an  amalgam,  though  if  liquid 
sodium  amalgam  is  used  the  aluminium  amalgam  is  readily 
formed.    Aluminium,  when  amalgamated,  is  easily  oxidized, 

391 


392  CHEMICAL  LECTURE  EXPERIMENTS 

and  in  the  presence  of  moist  air  aluminium  oxide  is  rapidly 
formed. 

A  character  or  letter  is  drawn  on  a  piece  of  sheet  alumin- 
ium, well  cleaned  and  free  from  oil,  by  using  a  clean  copper 
wire  dipped  in  liquid  sodtum  amalgam.  Almost  immediately 
a  mossy  growth  of  aluminium  oxide  appears,  rising  perpen- 
dicularly from  the  aluminium  sheet  in  sharply  cut  lines  to 
a  height  of  several  millimeters. 

Al  sheet ;  Cu  wire  5  Na  amalgam  (liquid). 

4.  Reduction  of  metallic  oxides  by  aluminium  powder.  — 

Ferric  oxide,  when  mixed  with  half  its  weight  of  aluminium 
powder  and  strongly  heated  in  a  crucible,  is  reduced  by  the 
aluminium  with  an  explosion.  The  powders  should  be  inti- 
mately mixed  and  placed  in  a  small  crucible,  and  a  disk  of 
asbestos  paper  should  be  pressed  down  upon  them.  As  con- 
siderable heat  is  required  to  start  the  reaction,  it  may  be 
necessary  to  use  the  blast-lamp. 

Lead  monoxide,  when  mixed  with  aluminium  powder  and 
heated,  is  likewise  reduced,  producing  an  explosion.  Four 
grams  of  litharge  are  mixed  with  .25  g.  of  aluminium  powder. 

Cupric  oxide  in  the  form  of  a  powder,  when  mixed  with 
one-third  its  weight  of  aluminium  powder,  also  explodes  on 
ignition. 

Small  crucibles ;  asbestos  paper ;  powdered  Al,  re203,  PbO,  and 
CuO. 

5.  Explosion  of  aluminium  powder  and  sodium  perox- 
ide. —  When  aluminium  powder  and  anhydrous  sodium 
peroxide  are  mixed  and  moistened  with  a  drop  of  water,  the 
mixture  explodes. 

Sodium  peroxide  is  placed  in  a  clean,  dry  test-tube  and 
an  equal  volume  of  aluminium  powder  added.  The  two 
powders  are  well  mixed  by  shaking,  and  the  test-tube  is 


ALUMINIUM  393 

clamped  behind  a  glass  screen.  One  drop  of  water  is  allowed 
to  flow  from  a  long  glass  tube  into  the  test-tube.  The  result- 
ing explosion  shatters  the  tube. 

Glass  screen ;  long  glass  tube  ;  Na202  ;  Al  powder, 

• 

6.  Union  of  aluminium  and  bromine.  — Aluminium  and 
bromine  while  not  uniting  in  the  cold  react  very  energeti- 
cally at  a  higher  temperature.  Aluminium  filings  are  placed 
in  the  bottom  of  a  test-tube  clamped  in  a  vertical  position. 
After  heating  until  the  glass  is  just  red,  10  drops  of  bromine 
are  carefully  poured  from  a  dry  test-tube  into  the  heated 
tube.  The  elements  unite  with  a  vivid  combustion,  yielding 
anhydrous  aluminium  bromide. 

On  cooling,  2  or  3  drops  of  water  may  be  allowed  to  fall 
into  the  tube,  where  they  react  with  the  anhydrous  bromide 
with  a  hissing  sound. 

2  Al  -f  3  Br^  =  2  AlBrg. 
Al  filings ;  Br. 

7.  Union  of  aluminium  powder  and  iodine.  —  One-fourth 
of  a  gram  of  aluminium  powder  is  heated  in  a  thick-walled 
test-tube  to  faint  reduess.  One-half  a  gram  of  finely  pow- 
dered iodine  is  shaken  into  the  tube  out  of  a  folded  paper. 
The  aluminium  unites  with  the  iodine  with  brilliant  combus- 
tion. If  the  Bunsen  flame  is  held  at  the  mouth  of  the  tube 
for  a  moment,  the  vaporized  aluminium  iodide  will  catch  fire 
and  burn.  On  cooling,  a  mass  of  aluminium  iodide  mixed 
with  some  uncombined  aluminium  will  be  seen  in  the  bottom 
of  the  tube. 

If  1  or  2  drops  of  water  are  allowed  to  fall  on  the 
cooled  aluminium  iodide  in  the  test-tube,  a  vigorous  action 
takes  place,  accompanied  by  great  heat. 

2  Al  +  3  I2  =  2  AII3. 
Al  powder ;  I. 


394  CHEMICAL   LECTURE   EXPERIMENTS 

8.  Absorptive  power  of  aluminium  hydroxide  for  coloring 
matter.  —  Aluminium  hydroxide  absorbs  certain  coloring 
matters,  and  this  property  is  much  used  in  the  process  of 
dyeing. 

An  infusion  of  logwood  is  prepared  by  boiling  for  two 
minutes  a  few  pieces  of  the  wood  with  water.  One  hundred 
cubic  centimeters  of  the  colored  liquid  are  placed  in  a  large 
mortar,  and  one-third  of  its  volume  of  a  thick  paste  of 
moistened,  well-washed,  freshly  precipitated  aluminium 
hydroxide  is  added.  The  mixture  is  rubbed  with  a  pestle 
for  several  minutes,  and  then  washed  upon  a  large  filter. 
Unless  a  too  concentrated  solution  of  logwood  has  been  used, 
the  filtrate  will  appear  perfectly  colorless. 

If  aluminium  hydroxide  is  precipitated  from  an  alum 
solution  which  is  somewhat  colored  with  logwood  extract, 
the  hydroxide  will  combine  with  the  coloring  matter  and 
settle  as  a  colored  precipitate,  leaving  the  supernatant 
liquid  clear.  The  alum  solution  should  be  distinctly 
colored,  and  then  aluminium  hydroxide  added  in  slight 
excess. 

Cotton  fibres,  when  boiled  with  logwood  extract,  absorb 
but  a  very  small  amount  of  the  coloring  matter.  If,  on  the 
other  hand,  the  fibres  are  impregnated  with  aluminium  salts, 
sufficient  color  is  deposited  on  the  fibre  to  make  the  process 
applicable  for  dyeing. 

A  strip  of  well-washed  white  cotton  cloth  is  soaked  in  a 
solution  of  aluminium  acetate,  prepared  by  dissolving  alu- 
minium.  hycwt)xi4e  in  an  insufficient  quantity  of  acetic  acid. 
The  strip  of  cl(1th,  together  with  a  fresh  strip,  is  immersed 
in  logwood  extract  and  boiled,  with  constant  stirring  for  a 
few  minutes.  The  cloth  impregnated  with  the  aluminium 
salt  will  acquire  a  deep  color. 

Mortar  and  pestle  ;  cotton  cloth  ;  logwood  chips  ;  A1(0H)3  paste  ; 
KA1(S04)3  solution. 


ALUMINIUM  395 

9.  Preparation  of  potassium  aluminium  sulphate  (potas- 
sium alum).  —  One  molecule  of  aluminium  sulphate  com- 
bines with  1  molecule  of  potassium  sulphate,  forming  a 
double  sulphate  which  crystallizes  with  24  molecules  of 
water.  Owing  to  its  relative  insolubility  in  water,  it  is 
readily  prepared  by  mixing  equal  volumes  of  saturated 
solutions  of  potassium  sulphate  and  aluminium  sulphate. 
On  shaking  the  test-tube,  a  crystalline  precipitate  is  obtained. 

A  saturated  solution  of  potassium  chloride  may  be  used, 
in  the  place  of  the  potassium  sulphate  solution,  with  the 
same  result. 

10.  Utilization  of  alum  in  clarifying  water.  —  When  a 
solution  of  alum  is  added  to  a  natural  water  which  is  slightly 
alkaline,  aluminium  hydroxide  is  precipitated  in  a  very  finely 
divided  condition,  and,  as  the  flocculent  precipitate  settles, 
it  entangles  with  it  any  solid  organic  matter  or  sediment 
which  may  be  present  in  the  water. 

A  few  cubic  centimeters  of  alum  solution  are  added  to 
some  turbid  water  in  a  2  1.  beaker,  and  the  solution  is  allowed 
to  stand  over  night.  A  second  beaker  should  be  filled  with 
the  water  and  no  alum  solution  added  to  it.  The  next  day 
it  will  be  found  that  the  beaker  containing  the  alum  solu- 
tion in  the  water  will  be  perfectly  clear,  all  the  impurities 
having  settled  to  the  bottom  with  the  aluminium  hydroxide. 
The  contrast  between  this  and  the  other  beaker  will  be  very 
marked. 

TW02I.  beakers,  turbid  water;  alum  so,  JT^    %    / 


TIN 


1.  Deposition  by  electrolytic  action.  —  A  small  porous 
cup  half  tilled  with  very  dilute  sulphuric  acid  is  placed  in  a 
beaker  containing  concentrated  stannous 
chloride  solution.  A  rod  of  zinc,  to  which 
a  copper  wire  is  attached,  is  placed  in  the 
porous  cup  and  the  end  of  the  copper  wire 
immersed  1  cm.  beneath  the  surface  of  the 
stannous  chloride  solution.  The  appara- 
tus thus  arranged  is  placed  in  a  quiet  spot 
and  covered  with  a  bell-jar.  In  the  course 
of  24  hours,  a  net-work  of  tin  crystals  will 
be  formed  in  the  liquid  surrounding  the 
porous  cup  (Fig.  158). 


Fig.  158 


600  cc.  beaker  ;  porous  cup  ;  Zn  rod  with  Cu  wire  ;  SnCl2  solution. 


2.  Deposition  on  zinc.  —  A  solution  of  stannous  chloride 
is  decomposed  by  the  action  of  metallic  zinc,  tin  being 
deposited  in  the  form  of  fine  crystals. 

A  zinc  rod  is  immersed  in  a  rather  concentrated  solu- 
tion of  stannous  chloride.  A  mossy  deposit,  consisting  of 
minute  crystals  of  tin,  forms  about  the  zinc. 

That  the  mossy  vegetation  obtained  by  immersing  a  strip 
of  zinc  in  tin  chloride  solution  consists  of  minute  crystals 
of  the  metal,  is  shown  by  firmly  pressing  a  quantity  of  the 


TIN  397 

spongy  mass  between  the  fingers  until  all  water  is  removed. 
The  crystals  knit  together  so  closely  that  the  mass  appears 
as  a  solid  lump,  which  may  be  polished  by  rubbing  with  a 
piece  of  chamois  skin. 

By  using  a  more  dilute  solution  of  the  chloride  and  allow- 
ing the  reaction  to  take  more  time,  larger  crystals  of  tin 
may  be  obtained,  and  a  treelike  deposit  will  be  formed. 

SnCla  +  Zn  =  Sn  +  ZnClg 
SnCl2 ;  Zn  rod. 

3.  Crystalline  structure.  —  On  bending  a  rod  of  tin  or  a 

piece  of  tin  pipe,  the  crystals  rub  on  each  other  producing 
a  peculiar  crackling  sound  called  the  "  tin  cry." 

When  molten  tin  is  allowed  to  cool,  it  assumes  a  crystal- 
line structure. 

A  piece  of  common  tinned  iron  is  heated  over  a  Bunsen 
burner  until  the  tin  begins  to  be  discolored.  It  is  then 
thrust  quickly  into  cold  water  and  the  surface  rubbed  with 
a  piece  of  filter-paper  moistened  with  dilute  aqua  regia. 
After  removing  the  excess  of  acid  by  rubbing  with  a  lit- 
tle dilute  sodium  hydroxide  solution,  the  surface  of  the 
metal  will  be  found  covered  with  well-marked  crystalline 
figures. 

Block  tin  rod  or  pipe  ;  sheet  tinned  iron. 

4.  Preparation  of  stannic  chloride.  —  Chlorine  when 
brought  in  contact  with  heated  tin  unites  with  it,  forming 
stannic  chloride. 

A  few  pieces  of  granulated  tin  are  placed  in  the  larger 
distilling  flask  shown  in  Fig.  159.  A  current  of  dry  chlorine 
is  conducted  through  the  glass  elbow  in  the  neck  of  the 
flask  and  caused  to  play  upon  the  surface  of  the  tin.  The 
side  tube  is  connected  with  a  small  distilling  flask  immersed 


398 


CHEMICAL  LECTURE  EXPERIMENTS 


in  ice- water.     The  excess  of  chlorine,  together  with  any  un- 

condensed  vapors 
of  stannic  chlo- 
ride, is  conducted 
to  a  flue. 

The  tin  is  care- 
fully heated  till  it 
melts,  when  it  will 
be  seen  that  the 
reaction  with  the 
chlorine  has  begun 
as  the  flask  fills 
with  dense  white 
fumes.  The  chlo- 
ride condenses  for 
Fig.  159  ,,  .  .     - 

the    most   part  m 

the  small  flask  to  a  light-colored,  fuming  liquid. 
Sn  -f  2  CI2  =  SnCl4. 
Apparatus  (Fig.  159)  ;  CI  generator  ;  Sn  ;  ice. 


5.  Action  of  stannic  chloride  in  the  air.  —  Stannic  chlo- 
ride fumes  strongly  in  the  air  and  rapidly  absorbs  moisture, 
forming  a  crystalline  hydrate. 

One  cubic  centimeter  of  stannic  chloride  is  poured  into 
a  dry  400  cc.  crystallizing-dish,  and  a  piece  of  filter-paper 
placed  over  it.  The  chloride  soon  absorbs  moisture  from 
the  air,  and  forms  a  solid  crystalline  mass  on  the  bottom 
and  sides  of  the  dish. 

Much  larger  crystals  are  obtained  by  pouring  1  cc.  of  the 
chloride  into  a  500  cc.  flask,  which  is  allowed  to  stand  over 
night.  The  stannic  chloride  will  slowly  evaporate  and,  ris- 
ing through  the  narrow  neck,  come  in  contact  with  the 
moisture  of  the  air  and  form  a  network  of  crystals  across 


TIN  399 

the  mouth  of  the  flask.  The  flask  is  filled  with  the  fumes 
of  stannic  chloride,  and  by  blowing  moist  air  through  a 
glass  tube  into  the  flask  dense  white  clouds  are  formed. 

400  cc.  crystallizing-dish,;  600  cc.  flask  ;  SnCU. 

6.  Stannous  iodide  from  stannous  chloride  and  potassium 
iodide.  —  When  concentrated  solutions  of  stannous  chloride 
a.nd  potassium  iodide  are  mixed,  a  yellow  crystalline  pre- 
cipitate of  stannous  iodide  appears  suddenly  in  the  solution. 

SnCls  +  2  KI  =  Snlg  +  2  KCl. 
Concentrated  solutions  of  SnCl2  and  KI. 

7.  Preparation  of   stannic    sulphide   (mosaic  gold).  —  A 

mixture  of  equal  parts  of  powdered  tin  and  sulphur  flowers 
is  mixed  with  one-eighth  of  its  volume  of  powdered  ammo- 
nium chloride.  The  mixture  is  then  placed  in  a  porcelain 
crucible,  covered  with  a  2  mm.  layer  of  powdered  ammonium 
chloride,  and  the  covered  crucible  heated  with  a  Bunsen 
burner.  As  a  result  of  the  reaction,  the  ammonium  chloride 
vaporizes  as  a  white  smoke,  and  stannic  sulphide  sublimes 
as  a  brilliant  yellow  crystalline  deposit  on  the  crucible  lid. 

Porcelain  crucible  ;  Sn  ;  S  flowers ;  NH4CI. 


LEAD 


1.  Preparation  of  pyrophoric  lead.  —  Finely  divided  lead 
ignites  spontaneously  when  exposed  to  the  air.  By  the 
ignition  of  lead  tartrate,  a  mixture  of  finely  divided  lead 
and  carbon  is  obtained. 

Five  grams  of  lead  tartrate  are  gently  heated  in  an  igni- 
tion tube  until  the  evolution  of  gas  ceases.  It  is  important 
that  the  heat  should  not  be  carried  to  too  high  a  degree,  as 
the  small  particles  of  lead  are  liable,  under  those  circum- 
stances, to  fuse  together  partially,  and  thus  spoil  the  experi- 
ment. As  soon  as  the  gases  cease  coming  off,  the  tube  is 
corked  with  a  well-fitting  rubber  stopper  to  insure  an 
air-tight  closure.  After  the  tube  has  become  perfectly  cold, 
the  cork  may  be  removed  and  the  finely  divided  lead  poured 
out  upon  a  plate,  best  from  a  height  of  half  a  meter.  On 
exposure  to  the  air,  the  lead  catches  fire  spontaneously. 

Preparation  of  lead  tartrate.  —  Lead  acetate  solution  is 
added  to  a  solution  of  tartaric  acid  till  there  is  no  more 
precipitate  formed.  The  precipitate,  which  is  quite  insoluble 
in  water,  may  be  filtered  off,  washed'  with  water,  and  dried 
in  an  air-bath.  It  loses  its  crystal  water  at  130'^,  and  in  this 
form  is  best  suited  for  the  above  experiment,  since  the  water 
is  likely  to  condense  and  break  the  tube. 

Hard-glass  test-tube  with  well-fitting  rubber  stopper  ;  white  plate  ; 
lead  tartrate. 

400 


LEAD 


401 


2.  Deposition  on  zinc  (lead  tree) .  —  The  deposition  of 
lead  from  a  solution  of  lead  nitrate  upon  a  zinc  rod  is 
obtained  by  covering  a  rod  of  zinc,  such  as  is 
used  in  batteries,  with  one  layer  of  asbestos 
paper.  The  rod  is  then  suspended  in  a  mod- 
erately strong  (10  per  cent)  solution  of  lead 
nitrate,  and  allowed  to  stand  till  the  next  exer- 
cise. Crystals  of  lead  will  appear  on  the  out- 
side of  the  rod  (Fig.  160). 

A  similar  rod,  not  covered  with  paper,  when 
dipped  into  a  solution  of  lead  nitrate,  is  im- 
mediately covered  with  a  black,  mossy  deposit 
of  finely  divided  lead. 

Pb(N03)2  +  Zn  =  Zn(N03)2  +  Pb. 

Asbestos  paper  ;  Pb(N03)2  solution  (10  percent)  ;  Zn  rods. 

3.  Crystalline  structure  of  lead.  —  If  a  piece  of  sheet-lead 
is  brushed  over  with  strong  nitric  acid,  a  crystalline  structure 
will  be  developed.  The  excess  of  acid  should  be  removed 
by  washing  with  water. 

As  the  lead  oxidizes  rapidly,  the  figures  soon  disappear. 

Sheet-lead ;  concentrated  HNOg. 


Fig.  160 


4.  Action  of  water  on  lead.  —  A  large  strip  of  clean,  bright 
lead  is  suspended  in  a  beaker  of  distilled  water  for  several 
hours.  A  white  precipitate  is  formed,  part  of  which  settles 
to  the  bottom,  while  quite  a  large  quantity  coats  the  lead, 
giving  it  a  corroded  appearance. 

Hydrogen  sulphide  added  to  the  water  produces  a  black 
precipitate  of  lead  sulphide. 

By  dissolving  slight  quantities  of  certain  salts  in  water  in 
different  beakers,  and  allowing  the  lead  to  remain  in  them, 
a  very  striking  comparison  may  be  made  of  the  respective 
2d 


402  CHEMICAL   LECTURE   EXPERIMENTS 

merits  of  potable  waters  containing  those  salts  when  used 
with  lead  pipes. 

The  above  described  experiment  is  repeated,  using  a  beaker 
containing  a  liter  of  water,  in  which  .30  g.  of  dry  potas- 
sium carbonate  and  .04  g.  of  potassium  nitrate  have  been 
dissolved.  After  standing  24  hours,  the  solution  is  tested 
with  hydrogen  sulphide.  While  in  the  beaker  of  pure  dis- 
tilled water  an  intense  black  is  formed,  the  water  containing 
the  salts  gives  no  reaction  with  hydrogen  sulphide,  since  the 
salts  entirely  prevent  any  solvent  action  of  the  water. 

2  large  beakers  ;  2  large  pieces  of  sheet  Pb  ;  distilled  water ;  K2CO3  ; 
KNO3. 

5.  Oxidizing  action  of  lead  peroxide.  —  (a)  On  sulphur. — 
When  dry,  freshly  prepared  lead  peroxide  is  rubbed  in  a 
mortar  with  a  small  bit  of  sulphur,  the  mixture  takes  fire. 

Gauntlets ;  mortar  and  pestle  ;  Pb02  ;  S  flowers. 

(h)  On  hydrogen  sulphide.  —  A  stream  of  hydrogen  sul- 
phide is  allowed  to  impinge  on  a  gram  or  two  of  dry,  freshly 
prepared  lead  peroxide.  On  coming  in  contact  with  the 
oxide,  the  gas  is  oxidized,  and  bursts  into  a  flame.  The 
surface  of  the  lead  peroxide  soon  turns  a  lighter  color,  owing 
to  the  formation  of  lead  sulphate.  By  stirring  the  powder, 
and  thereby  exposing  fresh  surfaces  to  the  action  of  the  gas, 
nearly  the  whole  mass  may  ultimately  be  converted  to  lead 
sulphate. 

The  powder  may  be  allowed  to  fall  by  the  end  of  a  tube 
through  which  hydrogen  sulphide  is  issuing.  The  gas  will 
be  ignited. 

H2S  generator ;  Pb02. 

(c)  On  nitrobenzene.  —  The  strong  oxidizing  action  of  lead 
dioxide  may  be  shown  by  heating  1  g.  of  the  substance 


LEAD  403 

with  2  or  3  drops  of  nitrobenzene  in  a  test-tube  clamped 
behind  glass  screens.  On  heating  the  tube  an  explosion 
occurs. 

Glass  screens  ;  Pb02  ;  nitrobenzene. 

6.  Explosion  of  lead  nitrate  and  sulphur.  —  Lead  nitrate, 
when  rubbed  with  sulphur,  oxidizes  it  with  explosive  vio- 
lence. 

Equal  quantities  of  finely  pulverized  lead  nitrate  and 
sulphur  flowers  should  be  placed  in  an  unglazed  mortar, 
and  rubbed  with  the  pestle  in  the  gloved  hand.  Very  small 
quantities  of  the  mixture  should  be  used. 

Mortar  and  pestle ;  gauntlets  ;  Pb(N03)2  ;  S  flowers. 


BISMUTH 


1.  Fusion  and  crystallization.  —  Bismuth  melts  at  a  com- 
paratively low  temperature  and,  on  cooling,  crystallizes  in 
rhombohedrons  which  appear  almost  cubical.  The  crystal- 
lization is  much  facilitated  by  heating  the  metal  for  some 
time  with  a  small  quantity  of  potassium  nitrate.  The 
fusion  is  made  in  a  porcelain  crucible  or  a  Jena  glass 
beaker.  As  soon  as  the  mass  has  cooled  sufficiently  to 
form  a  crust  on  the  surface,  a  hole  is  made  in  the  crust  and 
the  molten  metal  poured  out.  On  breaking  open  the  shell, 
the  cavity  will  be  found  to  be  lined  with  crystals. 

The  play  of  colors  observed  in  heating  and  cooling  copper 
(Ex.  5,  p.  332)  is  also  observed  in  heating  bismuth. 

Porcelain  crucible  or  Jena  glass  beaker ;  Bi ;  KNOg. 

2.  Fusible  alloys.  —  Tin  and  bismuth  form  ingredients 
of  all  of  the  fusible  alloys,  the  most  interesting  of  which  is 
the  so-called  Wood's  metal,  having  a  melting  point  of  about 
70°  C,  and  consequently  melting  in  hot  water. 

This  alloy  is  made  by  melting  together  15  g.  of  cadmium, 
20  g.  of  tin,  40  g.  of  lead,  and  80  g.  of  bismuth. 

Other  alloys  formed  by  varying  these  proportions  are 
Kose's  metal,  melting  at  93°.5,  and  Newton's  metal,  melting 
at  94°.5. 

Wood's  metal ;  Rose's  metal ;  Newton's  metal ;  Pb  ;  Bi ;  Cd  ;  Sn. 

404 


CHROMIUM 


1.  Preparation    of    anhydrous    chromium    chloride.  —  A 

mixture  of  equal  volumes  of  powdered  anhydrous  chro- 
mium oxide  and  charcoal  powder  is  placed  in  a  bulb-tube 
through  which  a  current  of  chlorine  is  being  passed.  On 
heating  the  mixture  strongly  with  a  large  flame,  a  violet 
crystalline  deposit  of  chromium  chloride  is  obtained  in  the 
colder  portions  of  the  tube. 

The  anhydrous  salt  is  insoluble  in  water. 

CrgOg  -f  3  C  +  3  CI2  =  2  CrClg  +  3  CO. 

Bulb-tube  ;  CI  generator ;  Cr208  ;  charcoal  powder. 

2.  Preparation  of  chromium  trioxide  (chromic  acid).  — 

Sixty  cubic  centimeters  of  concentrated  sulphuric  acid  are 
slowly  poured  into  40  cc.  of  a  cold  saturated  solution  of 
potassium  dichromate.  The  mixture  is  then  cooled,  and 
the  resulting  crystalline  precipitate,  consisting  of  chromium 
trioxide,  filtered  on  a  funnel  containing  glass  wool  or  fibrous 
asbestos. 

KaCrgOy  -f  H2SO4  =  K2SO4  +  2  CrOs  4-  H2O. 
Funnel ;  glass  wool ;  cold  saturated  solution  of  K2Cr207. 

3.  Oxidizing  action  of  chromium  trioxide.  —  (a)  On  alco- 
hol.—  If   absolute  alcohol  is  allowed  to  drop  upon  a  few 

405 


406       CHEMICAL  LECTURE  EXPERIMENTS 

crystals  of  dry  chromium  trioxide,  the  alcohol  is  oxidized 
and  ignited. 

CrOs  crystals  ;  absolute  alcohol. 

(6)  On  wood.  —  Chromic  acid,  or  potassium  dichromate 
in  the  presence  of  sulphuric  acid,. oxidizes  wood  to  carbon 
dioxide  even  in  the  cold.  A  splinter  of  wood,  when  thrust 
into  a  warm  solution  of  potassium  dichromate  and  sulphuric 
acid,  is  instantly  colored  brown,  and  small  quantities  of  a 
gas  are  evolved. 

Sawdust,  when  mixed  with  a  solution  of  potassium  dichro- 
mate and  sulphuric  acid,  is  rapidly  oxidized  to  carbon  diox- 
ide with  the  liberation  of  great  heat.  The  mixture  is  made 
in  a  500  cc.  flask,  fitted  with  a  one-holed  cork,  and  a  delivery- 
tube  dipping  into  lime-water.  In  a  few  moments,  even  with- 
out the  application  of  external  heat,  a  reaction  begins,  large 
quantities  of  carbon  dioxide  are  evolved,  and  the  mixture 
becomes  very  hot.  The  battery  solution  described  on  p.  3 
may  be  used  in  these  experiments  with  success. 

Splinter  ;  sawdust ;  K2Cr207  or  battery  solution  ;  lime-water. 

4.  Dyeing  with  chrome  yellow.  —  By  precipitating  chrome 
yellow  on  the  fibres  of  cloth,  the  color  is  sufficiently  re- 
tained to  dye  the  fabric. 

A  strip  of  well-washed  cotton  cloth  is  dipped  in  a  solution 
of  lead  acetate  and  then  immersed  in  a  solution  of  potassium 
dichromate.  The  cloth  becomes  covered  with  a  bright  yel- 
low, finely  divided  precipitate  of  lead  chromate. 

Cotton  cloth  ;  solutions  of  K2Cr207  and  Pb (€211302)2. 

5.  Oxidizing  action  of  lead  chromate Lead  chromate 

readily  gives  up  its  oxygen  when  heated  with  organic  mat- 
ter, and  is  much  used  as  an  oxidizing  agent  in  elementary 
organic  analysis. 


CHROMIUM  407 

A  small  quantity  of  pulverized  sugar  is  mixed  with  three 
or  four  times  its  volume  of  lead  chromate,  and  the  mixture 
is  heated  in  a  test-tube.  The  carbon  dioxide  may  be  con- 
ducted through  a  glass  tube  into  lime-water,  where  it  will 
produce  a  white  precipitate. 

Test-tube  with  cork  and  delivery-tube ;  sugar ;  PbCrO*  fused  and 
powdered;  lime-water. 

6.  Preparation  of  chromium  oxychloride  (chromyl  chlo- 
ride). —  When  a  mixture  of  sodium  chloride  and  potassium 
chromate  is  heated  with  concentrated  sulphuric  acid,  a  dark 
red  liquid,  chromium  oxychloride,  distils  over. 

Ten  grams  of  fused,  powdered  sodium  chloride  should  be 
heated  to  fusion  in  a  crucible  with  17  g.  of  potassium  chro- 
mate. The  cooled  mass  is  then  pulverized  and  placed  in  a 
500  cc.  glass-stoppered  retort,  the  neck  of  which  is  thrust 
into  a  filter  flask  used  as  a  receiver  (Fig.  93,  p.  223).  Thirty 
grams  of  fuming  sulphuric  acid  or  25  g.  of  concentrated 
sulphuric  acid,  mixed  with  5  g.  of  sulphur  trioxide,-  are 
poured  through  a  long-stemmed  funnel  or  thistle-tube 
upon  the  mixture  of  the  salts.  When  the  retort  is  gently 
warmed,  dense  red  fumes,  which  distil  over  and  condense 
in  the  receiver  to  a  dark -colored  liquid,  appear. 

The  oxidizing  action  of  chromium  oxychloride  may  be 
shown  by  dropping  a  1  or  2  mm.  piece  of  well-dried 
phosphorus  into  2  or  3  drops  of  the  liquid  placed  in 
the  test-tube  shown  in  Fig.  109,  p.  262.  As  the  phos- 
phorus comes  in  contact  with  the  liquid,  an  explosion  is 
obtained. 

A  current  of  hydrogen  sulphide,  directed  upon  a  small 
quantity  of  the  liquid  in  an  evaporating  dish,  is  immedi- 
ately oxidized  and  ignited. 

Ammonia  gas  likewise,  when  directed  upon  the  liquid, 
reacts  with  evolution  of  dense  fumes. 


408  CHEMICAL   LECTURE   EXPERIMENTS 

A  filter  paper  moistened  with  alcohol  is  touched  with  a 
drop  of  liquid.     The  alcohol  is  ignited. 

K2Cr04  +  2  NaCl  +  2  HgSO^  =  Na^SO,  +  K2SO4  +  CrOaClg  + 

2H2O. 

500  cc.  glass-stoppered  retort ;  filter  flask  ;  apparatus  (Fig.  109,  p. 
262) ;  H2S  generator ;  NHs  generator ;  fused,  powdered  NaCl ;  K2Cr04  ; 
alcohol ;  P. 


IRON 


1.  Reduction  of  ferric  oxide  by  hydrogen — Ferric  oxide 
is  reduced  to  metallic  iron  when  heated  in  a  current  of 
hydrogen.  If  the  temperature  at  which  the  reduction  is 
carried  out  is  not  too  high,  the  reduced  iron  is  pyrophoric. 

A  thin  layer  of  ferric  oxide  is  placed  in  a  20  cm.  length 
of  combustion-tubing  fitted  at  each  end  with  a  one-holed 
rubber  stopper  and  a  glass  tube.  A  current  of  well-washed 
hydrogen  is  passed  slowly  through  the  tube,  and  the  iron 
oxide  is  heated  to  as  low  a  temperature  as  will  suffice  to 
effect  the  reduction.  When  no  more  water  escapes  from 
the  open  end  of  the  tube,  the  reduction  is  complete  and  the 
reduced  iron  is  allowed  to  cool  in  a  current  of  hydrogen. 
On  shaking  a  small  quantity  of  the  cold  powder  upon  a 
plate,  it  will  rapidly  oxidize  and  glow  in  the  air. 

Some  of  the  cooled  powder  may  be  allowed  to  fall  upon 
a  small  heap  of  gunpowder.  The  precautions  described  in 
Ex.  3,  p.  330,  should  be  carefully  observed  here. 

Precipitated,  well-washed,  and  dried  ferric  hydroxide  is 
best  used  for  reduction  when  pyrophoric  iron  is  desired. 
The  combustion-tube  may  be  drawn  out  at  both  ends  and 
sealed  off  after  the  reduction  is  complete.  The  tube  thus 
prepared  can  be  kept  indefinitely  and  the  pyrophoric 
character  of  the  iron  remain  unchanged. 

FegOg  +  3  H2  =  2  Fe  -f  3  HgO. 

20  cm.  length  combustion-tubing ;  1-holed  stoppers ;  H  generator 
with  gas  washing-bottles  j  gunpowder  ;  FegOs  ;  Fe(0H)3. 

409 


410 


CHEMICAL    LECTURE   EXPERIMENTS 


2.  "  Passive  "  iron.  —  When  iron  is  immersed  in  fuming 
nitric  acid,  it  becomes  resistant  to  the  action  of  acids  and 
other  reagents,  being  in  the  so-called  passive  state.  The 
passivity  is  explained  as  the  result  of  a  thin,  resistant  coat- 
ing on  the  iron  of  either  iron  oxide  or  oxides  of  nitrogen. 

A  piece  of  sheet  iron  is  freed  from  all  oil  and  carefully 
cleaned.     The  iron  is  then  suspended  on  a  fine  platinum  wire 

and  is  completely  immersed  in 
fuming  nitric  acid.  As  the  iron 
enters  the  acid,  a  vigorous  evo- 
lution of  oxides  of  nitrogen  is 
obtained.  The  reaction  is,  how- 
ever, of  only  a  few  seconds'  du- 
The  iron  is  then  carefully  with- 
immersed  in  water,  and  then  in 
ordinary  concentrated  nitric  acid.  The 
iron  is  no  longer  acted  upon  by  the  acid. 
Iron  in  the  passive  state  loses  its  prop- 
erty of  depositing  copper  from  solutions 
of  copper  salts,  and,  when  immersed  in  a 
saturated  solution  of  copper  nitrate,  the 
iron  will  retain  its  original  grayish  color. 
The  iron  should  be  carefully  withdrawn 
from  the  solution  of  copper  nitrate,  and  then  sharply  struck 
on  one  edge  with  a  lead-pencil  or  glass  rod.  The  passivity 
is  destroyed  by  the  blow,  and  the  iron  is  immediately 
covered  with  a  red  film  of  copper  precipitated  from  the 
saturated  solution  of  copper  nitrate  adhering  to  the  iron. 
If  a  large  sheet  of  iron  is  used  and  the  blow  is  care- 
fully struck,  the  deposition  of  copper  will  proceed  from  the 
point  of  contact  and  rapidly  extend  all  over  the  surface  of 
the  iron  (Fig.  161). 

The  experiment  may  be  repeated,  removing  the  film  of 
copper  by  immersing  the  iron  in  dilute  nitric  acid.     The 


Fig.  161 


IRON  411 

iron  may  be  again  rendered  passive  by  immersion  in  fuming 
nitric  acid. 

The  sheet  iron  may  be  readily  prepared  by  removing  the 
coating  of  tin  on  a  piece  of  common  tinned  iron.  The  tin 
plate  should  be  immersed  in  hydrochloric  acid  until  all  the 
tin  has  been  dissolved. 

Sheet  iron  cleaned  and  freed  from  grease  ;  Pt  wire  ;  Cu(N03),^ ; 
fuming  HNO3. 

3.  Carbon  in  iron.  —  The  carbon  in  iron  may  be  separated 
by  dissolving  a  piece  of  cast-iron  in  hydrochloric  acid.  The 
insoluble  carbon  will  separate  as  a  black  powder.  The  pres- 
ence of  combined  carbon  as  iron  carbide  gives  rise  to  the 
formation  of  hydrocarbons,  which  are  noticeable  by  the  odor 
they  impart  to  hydrogen  obtained  by  the  action  of  hydro- 
chloric acid  on  iron. 

Cast-iron;  HCl. 

4.  Combustion  of  gunpowder  and  powdered  iron.  —  The 

comparative  combustibility  of  gunpowder  and  iron  powder 
may  be  shown  by  allowing  a  mixture  of  equal  weights  (one- 
tenth  of  a  gram  of  each)  to  fall  from  an  iron  spoon  through 
the  flame  of  burning  alcohol.  Fifteen  cubic  centimeters  of 
alcohol  are  poured  into  a  porcelain  evaporating-dish  and 
ignited.  As  the  mixture  of  gunpowder  and  iron  powder 
falls  through  the  flame,  the  iron  powder  burns  with  brilliant 
scintillations,  but  the  gunpowder  is  not  ignited.  As  the 
alcohol  is  burnt  out  of  the  dish,  the  gunpowder  remaining 
in  the  bottom  is  finally  ignited. 

Evaporating-dish  ;  gunpowder  ;  Fe  powder ;  alcohol. 

5.  Combustion  of  iron  powder  and  potassium  chlorate.  — 

A  mixture  of    2  parts  of  iron  powder  and  1  part  of  pow- 
dered potassium  chlorate  burns  when  ignited.    The  mixture 
should  be  placed  on  an  asbestos  paper  in  the  hood. 
Asbestos  paper ;  Fe  powder ;  KCIO3  ;  touch-paper. 


..^^^' 


# 


CHEMICAL   LECTURE   EXPERIMENTS 


6.  Reduction  of  ferric  oxide  by  aluminium. — When  alu- 
minium powder  is  mixed  with  anhydrous,  finely  powdered 
oxides  of  the  metals  and  the  mixture  ignited,  the  aluminium 

, ♦'■extracts  the  oxygen  from  the  oxide,  forming  aluminium  oxide 
axid  setting  free  the  metal.^ 
^ ;  This  reaction  is  especially  satisfactory  when  using  a  mix- 

,_,  fure  of  aluminium  powder  and  ferric  oxide.  The  two  pow- 
ders are  mixed  in  equal  volumes  and  ignited  with  a  2  cm. 
strip  of  magnesium  ribbon.  The  mixture  burns  brightly, 
leaving  a  white  residue  of  aluminium  oxide.  The  iron  in  the 
finely  divided  condition  immediately  burns  and  reoxidizes. 

If  a  quantity  of  the  mixture  of  the  two  powders  is  placed 
in  a  crucible  and  ignited  from  the  top,  the  reoxidation  of 
the  iron  is  not  so  immediate. 

FegOg  +  2  Al  =  AI2O3  4-  2  Fe. 

Fe203  powder ;  Al  powder ;  Mg  ribbon. 

7.  Action  of  light  on  potassium  ferricyanide.  —  The  reduc- 
tion of  potassium  ferricyanide  by  light  is  used  in  photogra- 
phy to  produce  "  blue-prints." 

A  solution  of  the  salt  is  mixed  with  a  solution  of  "  citrate 
of  iron  and  ammonia  "  and  unsized  paper  is  coated  with  the 
liquid.  When  dry  the  paper  is  sensitive  to  light,  and  if  a 
piece  is  exposed  to  bright  sunlight  in  a  photographic  print- 
ing frame  and  subsequently  washed  in  very  dilute  hydro- 
chloric acid,  a  coating  of  Prussian  blue  will  be  left  on  it. 
By  using  a  design  cut  out  of  paper  or  a  photographic  nega- 
tive, the  design  or  picture  may  be  reproduced. 

Photographic  printing  frame  ;  unsized  paper  ;  design  or  photograph 
negative  ;  citrate  of  iron  and  ammonia  ;  K3Fe(CN)e. 

1  This  reaction  is  the  basis  of  a  series  of  special  experiments 
recently  devised  by  Goldschmidt.  The  apparatus  and  materials  are  to 
be  had  of  any  dealer  in  chemical  supplies. 


¥'0^ 


ift 


'^ 


{k      %    ^^ 


^. 


^■^ 


COBALT  AND  NICKEL  Vci,    "^r^, 


1.  Deposition  of  cobalt  by  magnesium.  —  A  piece  of 
bright,  clean  magnesium  ribbon,  when  immersed  in  a  solu- 
tion of  cobalt  sulphate,  becomes  covered  with  a  blue-black 
deposit  of  metallic  cobalt.  The  salt  solution  should  not  con- 
tain too  much  free  acid. 

C0SO4  +  Mg  =  MgSO^  +  Co. 
C0SO4  solution  ;  Mg  ribbon. 

2.  Dehydration  of  cobalt  chloride  on  filter-paper.  —  Filter- 
paper  saturated  with  cobalt  chloride  and  exposed  to  the 
action  of  dry  air  undergoes  a  change  in  color,  so  much  so 
that  the  tint  is  an  approximate  indication  of  the  moisture 
content  of  the  air. 

Two  pieces  of  filter-paper,  which  have  been  previously 
soaked  in  concentrated  cobalt  chloride  solution  and  allowed 
to  dry  in  the  air,  are  suspended 
by  means   of  a  piece   of   thread 
and  a  bit  of  wax  to  the  interior 
of  each  of  2  bell-jars  (Fig.  162). 
The  jars  are  placed  on  plates,  the 
one  over  a  crystallizing  dish  con- 
taining water,  the  other  over  a 
crystallizing  dish  containing  an- 
hydrous calcium  chloride.     The  calcium  chloride  abstracts 
the  moisture  from  the  air,  and  the  paper  soon  acquires  a 

413 


f^\ 


.^^1 


Fig.  162 


414  CHEMICAL  LECTURE  EXPERIMENTS 

deep  blue  color,  while  the  paper  over  the  vessel  of  water  is 
unaffected  and  remains  red.  On  interchanging  the  2  bell- 
jars  the  colors  are  changed  on  both  papers. 

2  bell-jars;  2  plates;  2  crystallizing  dishes;  CaCl2  (anhydrous); 
C0CI2. 

3.  Sympathetic  ink.  —  A  word  is  written  on  a  piece  of 
white  paper  with  dilute  cobalt  chloride  solution.  When 
dry  the  word  is  not  visible.  On  heating  high  above  a  Bun- 
sen  flame  the  word  appears  in  blue  lines,  which  gradually- 
fade  on  cooling. 

4.  Preparation  of  potassium  cobalt  nitrite  (Fischer's  salt). 
—  A  characteristic  reaction  of  cobalt,  whereby  it  may  be. 
readily  distinguished  from  nickel,  is  its  formation  of  a  yel- 
low crystalline  precipitate  (potassium  cobaltic  nitrite)  with 
a  solution  of  potassium  nitrite. 

Cobalt  nitrate  solution  is  acidified  with  acetic  acid  and 
then  a  solution  of  potassium  nitrite  added.  On  standing 
over  night  a  yellow  crystalline  precipitate  of  the  double 
nitrite  will  be  formed. 

Co(N03)2;  KNO2. 

5.  Reduction  of  nickel  oxide  by  hydrogen.  —  The  reduc- 
tion of  nickel  oxide  and  the  pyrophoric  nature  of  the  finely 
reduced  metal  is  well  shown  by  heating  the  oxide  in  a  short 
length  of  combustion-tubing  in  a  current  of  pure  hydrogen. 
When  the  reduction  is  complete,  a  one-holed  cork  bearing  a 
short  piece  of  glass  tubing  should  be  inserted  in  the  open 
end  of  the  combustion-tube  and  the  nickel  allowed  to  cool 
in  a  current  of  hydrogen. 

The  color  change  from  green  nickel  oxide  to  black  nickel 
is  so  marked  that  the  green  rather  than  the  black  oxide 
should  invariably  be  used. 


COBALT   AND   NICKEL  415 

A  small  portion  of  the  still  hot  metal  remaining  in  the 
tube  after  the  reduction  is  complete  will  burn  when  allowed 
to  fall  through  the  air. 

Finely  divided  nickel,  resulting  from  the  reduction  of 
the  oxide,  is  readily  oxidized  in  the  air,  and  while,  when 
cold,  it  does  not  burn  with  the  brilliancy  of  pyrophoric  lead 
(Ex.  1,  p.  400),  sufficient  heat  will  be  generated  on  exposing 
the  metal  to  the  air  to  ignite  a  small  heap  of  gunpowder. 

A  few  grams  of  gunpowder  are  placed  on  a  square  of 
asbestos  paper,  and  the  cold  reduced  nickel  poured  out  of 
the  tube  upon  it. 

If  a  small  quantity  of  the  reduced  metal  is  poured  upon 
the  heads  of  2  or  3  matches,  they  will  also  become  ignited. 

NiO  +  Hs  =  H2O  +  Ni. 

H  generator  ;  combustion-tube ;  4-tube  burner ;  NiO  ;  gunpowder. 

6.  Deposition  of  nickel  by  electrolysis  (nickel  plating). 
—  A  polished  strip  of  sheet  copper  is  connected  to  the  zinc 
pole  of  a  bichromate  battery  and  immersed  in  a  solution  of 
ammonium  nickel  sulphate.  The  negative  pole  may  be  a 
piece  of  nickel  or  platinum.  On  closing  the  electric  circuit, 
a  gray  deposit  of  nickel  will  be  formed  on  the  copper 
electrode. 

Bichromate  battery ;  sheet  Cu ;  Pt ;  Ni ;  ammonium  nickel  sul- 
phate. 

7.  Oxidation  of  nickel  in  the  air.  — A  sheet  of  polished 
nickel,  when  heated  in  the  air,  becomes  covered  with  a  thin 
iridescent  coating  of  the  oxide. 

8.  Solubility  of  nickel  sulphide   in  sodium  sulphide.  — 

Hydrogen  sulphide  added  to  an  alkaline  solution  containing 
nickel  produces  a  deep  black  solution  without  the  formation 
of  a  precipitate. 


416  CHEMICAL   LECTURE   EXPERIMENTS 

Nickel  chloride  solution  is  treated  with  a  small  quantity 
of  tartaric  acid,  and  then  sufficient  sodium  hydroxide  solu- 
tion is  added  to  make  the  liquid  feel  soapy.  On  conducting 
a  current  of  hydrogen  sulphide  through  the  solution,  a  jet- 
black  solution  is  formed,  which,  even  on  boiling,  does  not 
yield  a  precipitate.  On  pouring  the  liquid  upon  a  filter,  the 
black  solution  runs  through  the  paper,  and  on  washing  the 
filter  with  hot  water  the  absence  of  any  precipitate  may  be 
seen. 

This  reaction  furnishes  an  excellent  means  of  distinguish- 
ing nickel  from  cobalt  in  solutions,  for  with  cobalt  the  sul- 
phide is  precipitated,  the  supernatant  liquid  remaining 
colorless. 

H2S  generator  ;  solutions  of  tartaric  acid  and  NiCl2. 

9.  Preparation  of  nickel  tetracarbonyl  by  the  action  of 
carbon  monoxide  on  reduced  nickel.  —  Carbon  monoxide, 
when  conducted  over  finely  reduced  nickel,  unites  with  the 
metal  at  the  ordinary  temperatures,  forming  nickel  tetra- 
carbonyl. The  vapor  passes  along  with  the  excess  of 
carbon  monoxide,  and  may  be  condensed  to  a  colorless 
liquid  if  conducted  through  a  tube  immersed  in  a  freezing- 
mixture. 

The  nickel  for  this  experiment  should  be  very  finely 
divided,  and  is  best  obtained  by  reducing  nickel  oxide 
mixed  with  fibrous  asbestos  and  loosely  packed  in  a  40  cm. 
length  of  combustion-tubing.  The  finely  powdered  nickel 
oxide  should  be  thoroughly  mixed  with  the  asbestos,  to 
which  a  large  quantity  of  the  powder  will  cling.  Hydro- 
gen, purified  by  being  passed  through  a  solution  of  potas- 
sium permanganate,  is  conducted  through  the  tube,  which 
is  then  heated  to  low  redness.  As  the  reduction  is  effected, 
the  green  nickel  oxide  becomes  converted  to  black  nickel. 
When  no  more  water  vapor  escapes  from  the  tube,  the  re- 


COBALT   AND   NICKEL 


417 


duction   may  be   considered   complete,  and  the  nickel   is 
allowed  to  cool  in  a  current  of  hydrogen. 

Carbon  monoxide  from  the  generator  (Ex.  12,  p.  298)  is 
conducted  through  a  calcium  chloride  drying-tube  and  then 
directly  through  the  tube  containing  the  reduced  nickel. 
The  issuing  gas  is  passed  through  a  long  glass  elbow  ex- 
tending nearly  to  the  bottom  of  a  test-tube  fitted  with  a 
two-holed  cork.  The  gas  issuing  through  a  shorter  elbow 
in  the  second  hole  of  the  cork  should  be  conducted  into  the 


w 


-^n*  ■^^^^^^^^^^m^mm^m^i^s^^,.  gD=-^Y^='-^ 


Fig.  163 


flue.     The  test-tube  should  be  immersed  in  a  freezing-mix- 
ture of  salt  and  ice  (Fig.  163). 

As  the  carbon  monoxide  comes  in  contact  with  the  nickel, 
the  temperature  of  the  tube  is  materially  increased,  indi- 
cating the  chemical  action.  The  gas  escaping  from  the  glass 
elbow  in  the  test-tube  consists  of  carbon  monoxide  contain- 
ing a  quantity  of  uncondensed  vapor  of  nickel  tetracar- 
bonyl,  which,  owing  to  its  poisonous  character,  should  not 
be  inhaled.  The  preparation  of  any  considerable  quantity 
of  the  tetracarbonyl  requires  too  long  a  time  for  demonstra- 
tion on  the  lecture  table,  though,  if  the  operation  is  begun 
before  the  hour,  2  or  3  cc.  may  be  obtained.  If  the  test-tube 
2e 


418  CHEMICAL   LECTURE  EXPERIMENTS 

is  somewhat  constricted  in  the  middle,  the  condensed  liquid 
may  be  sealed  oif  in  the  glass  tube. 

If  the  escaping  gas  is  conducted  into  the  base  of  a  Bunsen 
burner,  -the  flame  becomes  brilliantly  luminous  from  the  in- 
candescence of  fine  particles  of  nickel.  The  structure  of  the 
Bunsen  flame  is  markedly  shown  by  the  varying  intensity 
of  brilliancy  in  its  different  parts. 

The  escaping  gas  may  be  ignited  at  the  end  of  a  glass  jet, 
where  it  will  burn  brightly,  giving  a  green  smoke  consisting 
of  nickel  oxide.  If  a  white  porcelain  dish  is  held  in  the  up- 
per portion  of  the  flame,  a  green  deposit  of  nickel  oxide  will 
be  obtained,  while,  if  the  dish  is  depressed  on  the  flame, 
black  metallic  nickel  will  be  deposited. 

The  nickel  tetracarbonyl  vapor  is  easily  decomposed  by 
heat  into  nickel  and  carbon  monoxide,  and  consequently,  if 
the  glass  tube  through  which  the  gas  is  being  conducted  is 
strongly  heated,  a  black  metallic  deposit  of  nickel  will  be 
obtained,  and  the  luminosity  of  the  flame  will  be  diminished 
until  ultimately  the  blue  flame  of  carbon  monoxide  alone  is 
obtained.  By  gently  heating  the  tube,  a  mirror  possessing 
a  brilliant  metallic  lustre  will  be  formed.  The  brilliancy 
of  the  mirror  is  a  function  of  the  temperature,  and  if  the 
tube  is  heated  to  about  200°  C,  the  best  results  are  secured. 
By  attaching  a  Y-tube  to  the  tube  conducting  the  waste 
gases  the  gas  may  be  suddenly  switched  into  a  glass  tube 
which  has  been  heated  to  185°  in  an  air-bath.  Instantly 
the  interior  of  the  tube  becomes  coated  with  a  nickel  mirror. 

M  -f-  4  CO  =  Ni(C0)4. 

4-tube  burner  ;  40  cm.  length  combustion-tubing  ;  test-tube,  cork, 
and  elbows  ;  porcelain  dish  ;  air-bath  and  thermometer  ;  fibrous  asbes- 
tos ;  CO  generator  (Fig.  120,  p.  299);  H  generator  ;  gas  washing-bottle 
containing  KMn04  solution  ;  NiO  ;  ice  and  salt  freezing-mixture. 


APPENDIX 


BIBLIOGRAPHY 

Arendt,    R.,  Technik   der    Experimentalchemie.    3te   Auf. 

Hamburg,  1900.     (Voss.) 
Heumann,  K.,  Anleitung   zum   Experimentiren.     2te   Auf. 

Braunschweig,  1893.     (Vieweg.) 
Newth,  G.  S.,    Chemical  Lecture  Experiments.     2d  Edition. 

London,  1900.     (Longmans,  Green  &  Co.) 

The  following  works,  though  not  primarily  designed  for 
lecture  use,  are  especially  rich  in  experimental  sugges- 
tions :  — 

Faideau,  F.,  La  Chimie  Amusante.     Paris. 

Mixter,  W.  G.,     An  Elementary  Text-book  of   Chemistry. 

New  York,  1889.     (John  Wiley  &  Sons.) 
Rem  sen,  I.,  Inorganic  Chemistry  (Advanced  Course).     New 

York,  1889.     (Henry  Holt  &  Co.) 
von   Richter,   V.,      A   Text-book   of   Inorganic   Chemistry 

(translated  by  E.  F.  Smith).     Philadelphia.     (P.  Blak- 

iston  &  Co.) 
Roscoe  and  Schorlemmer,  A  Treatise  on  Chemistry.     Lon- 
don.    (Macmillan  &  Co.) 
Torrey,  J.,  Elementary  Studies  in  Chemistry.     New  York, 

1899.     (Henry  Holt  &  Co.) 
Williams,  R.  P.,  Elements  of  Chemistry.      Boston.     (Ginn 

&Co.) 

419 


420 


CHEMICAL    LECTURE   EXPERIMENTS 


Description  of  the  hydrogen  sulphide  generator  in  use  in 
the  laboratory  of  Wesleyan  University  :  — 

"  It  consists  principally  of  three  glass  bottles,  A,  B,  and 
(7,  each  provided  with  an  orifice  near  the  bottom.  A  is  the 
generator  proper,  whose  mouth  is  wide  so  as  to  admit  large 
lumps  of  iron  sulphide,  and  whose  height  is  about  three 
times  its  diameter.     It  has  a  capacity  of  about  16  liters. 


nU 


.:ljp 


Fig.  164 


Through  the  rubber  stopper  which  closes  its  mouth  passes 
the  gas  main,  controlled  by  the  main  cock,  F,  and  terminat- 
ing at  a  suitable  hood  in  as  many  distributing  cocks  as  may 
be  desired.  Students  have  access  to  the  distributing  cocks 
only.  Through  the  same  stopper  enters  the  acid-supply 
tube,  drawn  down  at  the  end  £"  to  a  jet  capable  of  delivering 


APPENDIX  421 

a  stream  of  acid  not  thicker  than  the  shank  of  an  ordinary 
pin.  This  jet  projects  as  little  as  possible  below  the  stopper. 
Through  the  tubulure  at  the  bottom,  with  its  inner  end  just 
flush  with  the  stopper,  passes  a  rather  thick-walled  tube 
controlled  below  by  a  pinch-cock,  as  shown.  By  means  of 
this  tube  the  spent  acid  is  delivered  either  into  a  sink  or 
waste-pipe  capable  of  thorough  flushing,  or  into  a  small  bot- 
tle, D,  connected  with  a  flue,  which  may  be  detached  just 
below  the  pinch-cock  and  emptied  as  required.  The  gener- 
ator bottle  is  charged  with  large  pieces  of  iron  sulphide 
until  completely  full,  and  should  not  be  allowed  to  become  less 
than  half  fall  before  recharging.  The  spent  acid  must  never 
be  allowed  to  accumulate  in  such  quantities  as  to  reach  the 
top  of  the  sulphide. 

'•  B  is  the  acid  reservoir,  wide  in  proportion  to  its  height, 
with  a  capacity  of  about  8  liters.  The  stopper  at  its  mouth 
admits  a  funnel  whose  neck  is  continued  by  a  glass  tube 
passing  to  the  bottom  of  the  bottle.  This  reservoir  is  con- 
nected with  a  flue  as  shown.  The  acid  used  is  commercial 
hydrochloric,  diluted  with  an  equal  volume  of  water.  A 
proper  charge  of  acid  is  the  amount  necessary  to  fill  B  half 
full  when  acid  is  running  from,  or  stands  at,  the  jet  E.  The 
height  at  which  the  reservoir  itself  is  fixed  depends,  of 
course,  largely  on  the  pressure  to  be  overcome  by  the  gas. 
A  difference  of  level  of  6  inches  between  the  bottom  of  B 
and  the  top  of  A  has  been  found  ample  for  ordinary  analyti- 
cal work. 

"  C  is  the  gas  reservoir,  designed  chiefly  to  retain  what- 
ever gas  is  made  after  the  distributing  cocks,  or  F,  are  closed. 
Like  B,  it  is  wide  and  low.  It  has  a  capacity  of  about  4 
liters.  Its  mouth  should  be  on  exactly  the  same  level  as 
that  of  A,  and  the  vertical  portions  of  the  tube  connecting 
C  and  A  are  made  as  short  as  possible. 

"  The  tubing  used  in  the  apparatus  is  of  glass.     The  rubber 


422  CHEMICAL    LECTURE   EXPERIMENTS 

stoppers  are  protected  with  a  thin  coating  of  paraffin,  crowded 
into  place  while  the  latter  is  still  warm  and  soft,  and  firmly 
wired.  The  rubber  connections  are  coated  within  with  par- 
affin (by  pouring  hot  paraffin  through  them  when  perfectly 
dry),  and  securely  wired." 

(W.  P.  Bradley,  in  Am.  Chem.  Journal,  XXI.,  370.) 


INDEX 


Absorption  of  coloring  matter  by 
aluminium  hydroxide,  394 ;  by 
bone-black,  293. 

Acetylene:  from  calcium  carbide, 
323 ;  from  ethylene  dibromide,  323 ; 
from  incomplete  combustion  of 
illuminating  gas,  324. 

Actinic  action  of  light,  87,  90,  91, 
217,  ;38o,  412. 

Air :  analysis  of,  186 ;  carbon  dioxide 
in,  .306,  307  ;  combustion  in  hydro- 
gen, 343;  combustion  in  illuminat- 
ing gas,  341,  343,  345  ;  explosion 
with  hydrogen,  66;  quantitative 
combustion  of  iron  in,  27;  quan- 
titative comhustion  of  magnesium 
in,  27  ;  quantitative  combustion  of 
phosphorus  in,  29. 

Alloys :  fusible,  404. 

Alum :  use  in  clarifying  water,  395. 

Aluminium:  action  with  sodium 
hydroxide,  43 ;  amalgam,  391 ; 
combustion  in  air,  391 ;  combustion 
in  oxygen,  21,  391 ;  explosion  with 
oxygen ,  25 ;  explosion  with  sodium 
peroxide,  392;  reduces  metallic 
oxides,  392,  412;  union  with 
bromine,  393 ;  union  with  iodine, 
393. 

Aluminium  hydroxide :  absorptive 
power  for  coloring  matter,  394. 

Amalgam :  aluminium,  391 ;  ammo- 
nium, 358 ;  iron,  381 ;  sodium,  358 ; 
zinc,  3.  . 


Ammonia:  absorption  by  charcoal, 
197 ;  absorption  by  fused  calcium 
chloride,  197;  absorption  by  silver 
chloride,  198  ;  action  with  carbon 
dioxide,  362;  action  with  hydro- 
chloric acid,  193,  359;  action  with 
hydrogen  sulphide,  360;  action 
with  mercurous  nitrate,  194 ;  col- 
lection, 195;  combustion  in  air, 
198;  combustion  in  oxygen,  199; 
combustion  of  oxygen  in,  199; 
decomposition,  200-203;  drying  of, 
192, 196 ;  from  ammonium  chloride 
and  slaked  lime,  192 ;  from  ammo- 
nium hydroxide,  192 ;  from  ammo- 
nium hydroxide  and  potassium 
hydroxide,  191;  from  hydrogen 
and  nitric  oxide,  190 ;  from  organic 
substances,  189,  190;  from  potas- 
sium nitrate,  potassium  hydroxide, 
and  iron,  190 ;  solubility  in  water, 
194-196;  specific  gravity,193;  tests 
for,  193;  volumetric  relation  of 
nitrogen  in,  203;  water,  ammo- 
nium hydroxide,  196. 

Ammonium  amalgam,  358. 

Ammonium  carbamate,  362. 

Ammonium  carbonate :  preparation, 
362. 

Ammonium  chloride :  electrolysis 
of,  205 ;  from  ammonia  and  hydro- 
chloric acid,  359. 

Ammonium  dichromate:  decomposi- 
tion, 181,  361. 


423 


424 


.    INDEX 


Ammonium  hydroxide:  electrolysis 
of,  201 ;  preparation,  196. 

Ammonium  nickel  sulphate:  elec- 
trolysis of,  415. 

Ammonium  nitrate:  decomposition 
by  heat,  208;  decomposition  by 
zinc  dust,  361. 

Ammonium  nitrite :  formation,  180. 

Ammonium  sulphate:  dissociation 
of  solution,  360;  electrolysis  of, 
358. 

Ammonium  sulphide :  formation,  360. 

Anti-bleach,  152. 

Antimoniuretted  hydrogen :  see 
stibine,  273. 

Antimony:  combustion  in  air,  273; 
combustion  in  chlorine,  275;  depo- 
sition from  burning  stibine,  274; 
fusibility,  273;  spots,  274;  union 
with  bromine,  107. 

Antimony  cinnabar,  277. 

Antimony  hydride :  stibine,  273. 

Antimony  pentachloride,  275. 

Antimony  sulphide,  146 ;  action  with 
hydrochloric  acid,  139;  combus- 
tion in  oxygen,  275 ;  combustion 
in  potassium  nitrate,  276 ;  in  Ben- 
gal fires,  276. 

Antimony  trichloride,  276. 

Arsenic :  combustion  in  oxygen,  272 ; 
deposition  from  burning  arsine, 
270,  271,  274,  275;  purification, 
268;  solubility  in  sodium  hypo- 
chlorite, 274 ;  spots,  271,  274,275; 
sublimation,  269;  union  with  bro- 
mine, 107. 

Arsenic  hydride :  arsine,  269, 274, 275. 

Arsenic  iodide,  268. 

Arsenic  sulphide:  in  white  fire,  271. 

Arsenic  trioxide :  action  with  nitric 
acid,  218;  from  arsenic  and  oxy- 
gen, 272. 

Arseniuretted  hydrogen :  see  arsine, 
269. 

Asbestos:  deflagrating-spoon,  372; 
paper,  4,  331;  platinized,  61,  159, 
190. 

Aspirator,  6. 


Balloons,  49,  50. 

Barium  chlorate;  deflagration,  370. 

Barium  nitrate:  deflagration  on 
charcoal,  370 ;  in  green  fire,  370. 

Barium  oxide  :  absorption  of  oxygen 
by,  367;  action  with  sulphur  tri- 
oxide, 163,  369. 

Barium  peroxide:  action  with  hy- 
drogen, 368;  action  with  sulphuric 
acid,  75;  decomposition  by  heat, 
368;  ozone  from,  31;  preparation, 
367. 

Barium  sulphate:  from  barium  ox- 
ide and  sulphur  trioxide,  163,  369 ; 
solubility  in  water,  369. 

Batteries:  electric,  3. 

Battery  solution,  3. 

Bengal  fires:  preparation,  276,  357. 

Bismuth:  crystallization,  404;  fu- 
sion, 404;  in  alloys,  404. 

Bleaching:  by  chlorine,  86;  by  hy- 
drogen peroxide,  78 ;  by  hydrogen 
persulphide,  147 ;  by  hydrosulphu- 
rous  acid,  158;  by  perchloric  acid, 
105 ;  by  sodium  hypochlorite,  101 ; 
by  sulphur  dioxide,  155. 

Blue  prints,  412. 

Bone-black,  293,  294. 

Boric  acid:  coloration  of  alcohol 
flame,  281 ;  decomposition  of  so- 
dium chloride,  281 ;  dehydration, 
280;  preparation,  280. 

Boric  anhydride:  action  on  water, 
280;  reduction  by  magnesium, 
278. 

Boron :  combustion  in  air,  278 ;  prep- 
aration, 278. 

Boron  trifluoride,  279. 

Brass:  action  of  chlorine  on,  88. 

Bromine:  action  with  hydrogen  sul- 
phide, 108;  action  with  hydrogen 
phosphide,  256;  action  with  naph- 
thaline, 110;  from  potassium  bro- 
mide, 106;  solidification,  107; 
union  with  aluminium,  393;  union 
with  antimony,  107 ;  union  with 
arsenic,  107  ;  union  with  ethylene, 
322 ;  union  with  phosphorus,  263 ; 


INDEX 


425 


union  with  potassium,  354 ;  vapori- 
zation, 107 ;  water,  107. 

Bunsen  burner,  329. 

Burner :  for  oxyhydrogen  flame,  G4. 

Cadmium  :  combustion  in  air,  379 ; 
distillation,  379;  oxide,  379;  sul- 
phide, 146,  379. 

Calcium  carbide,  323. 

Calcium  carbonate :  action  with  hy- 
drochloric acid,  304;  decomposi- 
tion by  heat,  365. 

Calcium  chloride  :  absorption  of 
ammonia  by  fused,  197 ;  use  as 
drying  agent,  46,  120,  147. 

Calcium  fluoride:  action  with  sul- 
phuric acid,  127,  279. 

Calcium  hydroxide  :  action  with 
ammonium  chloride,  192 ;  action 
with  zinc  dust,  43. 

Calcium  hypochlorite,  100. 

Calcium  light,  65. 

Calcium  oxide:  action  with  water, 
363  ;  formation,  366  ;  incandes- 
cence of,  65 ;  use  as  drying  agent, 
363. 

Calcium  phosphide:  action  with 
water,  252,  253,  258;  preparation, 
364. 

Calcium  polysulphide,  147. 

Calcium  sulphate :  hydration,  365. 

Candle:  Christmas,  4;  combustion 
in  oxygen,  18;  increase  in  weight 
on  burning,  28. 

Carbon:  absorbs  coloring  matter, 
293 ;  electrical  conductivity,  291 ; 
in  iron,  411;  oxidation  at  low 
temperatures,  296;  oxidation  by 
sodium  peroxide,  351. 

Carbon  dioxide :  action  with  ammo- 
nia, 362 ;  extinguishes  candle 
flame,  314,  315 ;  freezing  mercury 
with  solid,  310;  from  baking-pow- 
der, 305;  from  calcium  carbonate 
and  hydrochloric  acid,  304;  from 
charcoal  and  oxygen,  303;  from 
fermentation,  305 ;  from  magnesite, 
304 ;  from  oxalic  acid,  298 ;  in  air, 


306,  307;  in  beverages,  306;  in  ex- 
pired air,  307;  liquefied,  307; 
preparation  of  solid,  307, 308 ;  prep- 
aration of  supersaturated  solu- 
tion, 316;  reduction  by  carbon, 
296;  reduction  by  magnesium, 
272;  reduction  by  zinc,  297;  rotates 
paper  wheel,  313;  siphoning,  314; 
specific  gravity,  311,  312, 313 ;  volu- 
metric relation  to  oxygen  con- 
sumed, 303. 

Carbon  disulphide :  action  with  nitric 
acid,  225;  cold  produced  by  evap- 
oration of,  317;  combustion  in 
nitric  oxide,  217;  combustion  in 
oxygen,  318;  combustion  of  iron 
in,  319;  combustion  of  potassium 
in,  318 ;  dissolves  fats,  317 ;  explo- 
sion with  oxygen,  318;  inflamma- 
bility, 317. 

Carbon  monoxide:  absorption  by 
cuprous  chloride,  301 ;  action  on 
palladious  chloride,  302;  action 
on  reduced  nickel,  416;  explosion 
with  oxygen,  301 ;  from  carbon 
dioxide  and  carbon,  296;  from 
carbon  dioxide  and  zinc,  297 ;  from 
oxalic  acid,  298;  from  sulphuric 
acid  and  potassium  ferrocyanide, 
298;  reduces  iodic  acid,  303;  re- 
duces silver  salt  solutions,  302. 

Chamber  crystals:  decomposition, 
167;  formation,  165,  167,  172, 
222. 

Charcoal:  absorbs  ammonia,  197; 
absorbs  hydrogen  sulphide,  292; 
action  with  sulphuric  acid,  151; 
combustion  in  liquid  nitrogen  per- 
oxide, 221 ;  combustion  in  nitric 
oxide,  217;  combustion  in  oxygen, 
18,  19;  combustion  in  perchloric 
acid,  105;  effects  combustion  of 
phosphorus,  288;  explosion  with 
oxygen,  25;  preparation,  291;  use 
in  gunpowder,  .356. 

Chemical  harmonica,  60. 

Chloric  acid,  104. 

Chloride  of  lime,  100. 


426 


INDEX 


Chlorine:  absorption  in  water,  84; 
action  on  brass,  88;  action  on 
ethylene,  322;  action  on  hydro- 
bromic  acid,  111 ;  action  on  hydro- 
gen phosphide,  355;  action  on 
iodo-starch  paper,  83;  action  on 
mercuric  iodide,  98,  99;  action 
on  phosphorus,  259,  261 ;  action  on 
silicon,  287;  action  on  sulphur, 
148;  action  on  turpentine,  86; 
bleaching  action ,  86 ;  by  Deacon's 
process,  82;  combustion  of  anti- 
mony in,  275;  combustion  of 
candle  in,  86;  combustion  of  hy- 
drogen in,  85;  crystalline  hydrate 
of,  84;  explosion  with  hydrogen, 
85;  from  hydrochloric  acid  and 
manganese  dioxide,  80;  from  hy- 
drochloric acid  and  potassium 
dichromate,  82;  generator,  80; 
manipulation,  81 ;  union  with  tin, 
397. 

Chlorine  monoxide:  action  with 
phosphorus,  99;  action  with  sul- 
phur flowers,  99;  explosion,  99; 
from  mercuric  oxide  and  chlorine, 
98. 

Chlorine  peroxide:  action  with 
alcohol,  103;  action  with  phospho- 
rus, 103 ;  action  with  sugar,  102 ; 
from  hydrochloric  acid  and  potas- 
sium chlorate,  102 ;  from  potassium 
chlorate  and  sulphuric  acid,  101. 

Chlorine  water:  decomposition  by 
light,  87;  preparation,  84. 

Chlorophyl  of  green  leaves  :  oxygen 
from,  13. 

Chrome  yellow  :  dyeing  with,  406. 

Chromic  acid,  405. 

Chromium  chloride:  preparation  of 
anhydrous,  405. 

Chromium  oxychloride  :  oxidizing 
action,  407;  preparation,  407. 

Chromium  trichloride :  oxidizing 
action,  405;  preparation,  405. 

Chromyl  chloride,  407. 

Cinnabar:  antimony,  277;  artificial, 
382. 


Coal:  distillation,  325;  gas,  324;  tar, 
325. 

Cobalt:  chloride,  413;  deposition  by 
magnesium,  413;  sulphide,  146. 

Collodion:  balloon,  49;  for  protect- 
ing corks,  81. 

Colored  fires:  blue,  387;  green,  370; 
purple,  357;  red,  3(57;  white,  271. 

Combustion:  reciprocal,  339;  spon- 
taneous, 238,  251,  284,  400;  under 
water,  103,  240. 

Copper:  action  on  nitric  acid,  211; 
action  on  sulphuric  acid,  151 ; 
action  of  salts  with  hydrochloric 
acid  and  air,  82;  color  of,  385; 
deposition  of  metallic,  14;  deposi- 
tion on  iron,  384;  electrical  depo- 
sition, 384;  melting,  65;  precipi- 
tation by  phosphorus,  245 ;  prepa- 
ration of  reduced  spiral,  385; 
union  with  sulphur,  134. 

Copper  phosphide,  245. 

Copper  sulphate :  electrolysis  of,  13, 
384. 

Cupric  chloride:  solubility  in  alco- 
hol, 386;  use  in  colored  fire,  387. 

Cupric  oxide:  reduction  by  alcohol, 
385 ;  reduction  by  hydrogen,  62, 63. 

Cuprous  chloride:  absorbs  carbon 
monoxide,  301 ;  action  of  light  on, 
385 ;  flame  coloration  by,  386. 

Cuprous  hydride,  158. 

Davy  Sabety  Lamp,  334. 

Deacon's  process  for  preparing  chlo- 
rine, 82. 

Deflagrating-spoon :  asbestos,  372; 
reversible,  371. 

Diamond :  combustion  in  oxygen, 
295. 

Diffusion  of  gases :  of  chlorine  and 
hydriodic  acid,  123;  of  hydrogen, 
55,  56,  57;  of  hydrogen  sulphide 
and  sulphur  dioxide,  143 ;  of  nitric 
oxide  and  air,  215;  separation  of 
hydrogen  and  oxygen  by,  58. 

Dissociation  of  ammonium  sulphate, 
360. 


INDEX 


427 


Drummond  light,  64. 

Drying  of  gases:  by  calcium  chlo- 
ride, 4(i;  by  quicklime,  192;  by 
soda-lime,  192;  by  sulphuric  acid, 
4«,  174. 

Dutch  metal,  88. 

Electrolysis  :  of  ammonium  chlo- 
ride, 205;  of  ammonium  hydroxide, 
201 ;  of  ammonium  nickel  sulphate, 
415;  of  ammonium  sulphate,  358; 
of  copper  sulphate,  13,  384 ;  of  hy- 
drochloric acid,  94,  96;  of  hydro- 
gen peroxide,  77;  of  silver  cya- 
nide, 388 ;  of  silver  nitrate,  388 ;  of 
stannous  chloride,  35)6 ;  of  sulphu- 
rous acid,  157  ;  of  water,  71,  72. 

Electrolytic  apparatus,  74;  Hoff- 
mann's, 72,  95. 

Erlenmeyer  flask,  2. 

Etching  glass,  128. 

Ether  thermometer,  174. 

Ethylene :  absorption  by  cold  water, 
322;  decomposition  by  heat,  321; 
dibromide,  322;  dichloride,  322; 
from  alcohol  and  sulphuric  acid, 
320;  from  ethylene  dibromide, 
321;  union  with  bromine,  322; 
union  with  chlorine,  322. 

Euchlorine,  26. 

Explosion:  of  hydrogen  generator, 
68,  69. 

Eyeglasses,  colored,  5. 

Fermentation  :  carbon  dioxide 
from,  305. 

Ferric  oxide:  action  on  potassium 
chlorate,  9;  reduction  by  alu- 
minium, 412;  reduction  by  hydro- 
gen, 409. 

Ferrous  sulphate:  formation,  384; 
solubility  of  nitric  oxide  in,  213. 

Ferrous  sulphide :  action  with  acids, 
137;  formation,  133,  1^,  144,  319. 

Fire-damp  indicator,  56. 

Fischer's  salt,  414. 

Flame:  Bunsen,  329,  334,  335,  337; 
carburetting   hydrogen,    336;    in- 


crease in  brilliancy  of  non-lumi- 
nous, 338;  luminosity  of,  335,  336, 
337;  pictures  of,  331,  332;  struc- 
ture, 198,  330. 

Flashlight  cartridges,  375. 

Fountain  produced  by  absorption :  of 
ammonia  in  water,  194;  of  hydro- 
chloric acid  gas  in  water,  94;  of 
nitrogen  peroxide  in  water,  216. 

Freezing-mixture  of  sodium  sulphate 
and  hydrochloric  acid,  352. 

Fuming:  nitric  acid,  221;  sulphuric 
acid,  160. 

Galvanized  iron,  378. 

Gases:  absorption  by  bone-black, 
293 ;  collection  by  displacement,  17, 
305  ;  collection  from  interior  of  can- 
dle flame,  333;  cylinders  of  com- 
pressed, 4;  drying,  46,  174,  192; 
ignition  of,  from  extinguished 
candle,  332. 

Gasometers,  14,  15. 

Gauntlets,  5. 

Generator,  Kipp,  3. 

Glass :  etching,  128 ;  Jena,  2. 

Glover  tower,  169,  170,  173. 

Gold:  precipitation  by  phosphorus, 
245 ;  reduction  of  chloride  by  phos- 
phorous acid,  261,  264. 

Graphite :  combustion  in  oxygen,  294. 

Guncotton,  207. 

Gunpowder:  combustion  with  iron 
powder,  411 ;  preparation,  356. 

Hoffmann  electrolytic  apparatus, 
72,  95. 

Hydrazine  sulphate:  action  with 
nitric  acid,  229 ;  action  with  potas- 
sium iodate,  229 ;  action  with  silver 
nitrite,  230;  decomposition  by 
heat,  229;  reducing  action,  228. 

Hydrazoic  acid,  229. 

Hydriodic  acid:  decomposition  by 
chlorine,  122;  decomposition  by 
heat,  121 ;  from  hydrogen  and 
iodine,  117 ;  from  iodine  and  rosin, 
119;   from  phosphorus  iodide  and 


428 


INDEX 


water,  118;  oxidation  by  nitric 
acid,  122;  purification,  119;  solu- 
bility in  water,  120,  121. 

Hydrobromic  acid :  action  with  am- 
monia, 111 ;  decomposition  by 
chlorine,  111;  from  bromine  and 
hydrogen,  108;  from  bromine  and 
hydrogen  sulphide,  108;  from  bro- 
mine and  naphthaline,  110;  from 
potassium  bromide,  109;  hygro- 
scopic nature,  111;  purification, 
109,  110;  solubility  in  water.   111. 

Hydrochloric  acid :  analysis  of  gases 
obtained  by  electrolysis  of,  98; 
electrolysis  of,  94,  96;  from  com- 
mercial acid,  92 ;  from  hydrogen  and 
chlorine,  89;  from  sulphuric  acid 
and  ammonium  chloride,  92 ;  from 
sulphuric  and  hydrochloric  acids, 
93;  from  sulphuric  acid  and  sodium 
chloride,  91 ;  generation  of  heat  by 
absorption  in  water,  93;  prepara- 
tion of  aqueous,  94 ;  solubility  in 
water,  93;  union  with  ammonia, 
359. 

Hydrofluoric  acid:  action  on  boric 
anhydride,  279;  action  on  glass, 
128,  129 ;  action  on  silicon  dioxide, 
289;  preparation,  127. 

Hydrofluosilicic  acid,  289. 

Hydrogen :  action  on  barium  perox- 
ide, 368;  action  on  magnesium 
nitride,  376 ;  burning  removes  oxy- 
gen from  air,  182;  carburetting 
flame  of,  336;  collection,  45;  com- 
bustion in  air,  59;  combustion  in 
chlorine,  85;  combustion  in  ni- 
trous oxide,  210 ;  combustion  of  air 
in,  343;  combustion  of  oxidizing 
agents  in,  346;  conductivity  for 
heat,  53,  determination  of  specific 
gravity,  48;  diffusibility,  55;  dif- 
fusion and  fire-damp  indicator,  56 ; 
diffusion  from  oxygen,  58;  diffu- 
sion out  of  porous  cup,  55 ;  diffu- 
sion producing  a  fountain,  56; 
diffusion  through  rubber,  57 ;  dry- 
ing, 46;    explosion   with  air.  66: 


explosion  with  chlorine,  85 ;  explo- 
sion with  nitrous  oxide,  210;  ex- 
plosion with  oxygen,  69;  flame, 
59;  from  aluminium  and  sodium 
hydroxide,  43;  from  calcium  hy- 
droxide and  iron  powder,  43 ;  from 
calcium  hydroxide  and  zinc  dust, 
43;  from  sodium  and  water,  39, 
350;  from  sodium  hydroxide  and 
iron,  42;  from  water  vapor  and 
iron,  41 ;  from  water  vapor  and 
magnesium,  42;  from  water  vapor 
and  zinc,  42 ;  from  zinc  and  hydro- 
chloric acid,  43;  from  zinc  and 
sulphuric  acid,  43;  ignition  by 
platinized  asbestos,  61 ;  non-con- 
ductivity for  sound,  54;  purifica- 
tion, 46;  siphoning,  60;  specific 
gravity,  47,  48;  soap-bubbles,  52; 
testing,  45  ;  use  in  balloons,  49-51. 

Hydrogen  generator :  care  in  testing, 
67 ;  danger  of  premature  lighting, 
68;  explosion  of ,  67-69. 

Hydrogen  peroxide:  action  on  lead 
sulphide,  76 ;  action  on  potassium 
dichr ornate,  76;  bleaching  action, 
77 ;  electrolysis  of,  77 ;  from  ba- 
rium peroxide  and  sulphuric  acid, 
76;  from  cooling  hydrogen  flame, 
74;  from  sodium  peroxide  and 
water,  75;  oxidizing  action,  77. 

Hydrogen  persulphide:  action  with 
silver  oxide,  148 ;  bleaching  action, 
147;  decomposition,  147;  prepara- 
tion, 147;  solubility  in  carbon 
disulphide,  147. 

Hydrogen  phosphide:  action  with 
bromine  vapor,  256;  action  with 
iodine,  258;  combustion  in  air, 
255;  combustion  in  oxygen,  257; 
from  calcium  phosphide  and  water, 
252,  253;  from  hydrogen  and  red 
phosphorus,  249;  from  phosphorus 
and  potassium  or  sodium  hydrox- 
ide, 250 ;  ignition  by  chlorine,  255 ; 
ignition  by  heat,  255 ;  ignition  by 
nitric  acid,  255;  ignition  by  silver 
nitrate  solution,  256 ;  purification, 


INDEX 


429 


250,  254;   spontaneous   inflamma- 
bility, 250. 

Hydrogen  sulphide:  absorption  by 
charcoal,  292;  action  with  bro- 
mine, 108;  action  with  solutions 
of  metallic  salts,  145 ;  action  with 
sulphur  dioxide,  143;  collection, 
139;  combustion  in  air,  142;  com- 
bustion of  iron  in,  144;  decompo- 
sition by  heat,  142 ;  decomposition 
by  sodium,  145;  description  of 
large  generator,  420 ;  drying,  137 ; 
explosion  with  oxygen,  143;  from 
antimony  sulphide,  139;  from  fer- 
rous sulphide,  137 ;  from  hydrogen 
and  sulphur,  135 ;  ignition  by  ni- 
tric acid,  144;  incomplete  combus- 
tion, 142;  manipulation,  138;  oxi- 
dation by  lead  peroxide,  402 ;  solu- 
bility in  sodium  hydroxide,  141 ; 
solubility  in  water,  140;  test  for, 
136;  union  with  ammonia,  360. 

Hydrosulphurous  acid :  bleaching 
action,  158;  preparation,  157. 

Hydroxylamine :  alternate  reducing 
and  oxidizing  action,  207;  reduc- 
ing action,  207. 

Hypochlorous  acid :  action  on  silver 
oxide,  101 ;  from  calcium  hypo- 
chlorite, 99;  from  chlorine  .  and 
mercuric  oxide,  99. 

Hypophosphorous  acid :  preparation 
of  sodium  or  potassium  salts,  250, 

251,  266. 

Illuminating  gas :  combustion  in 
nitric  acid,  225;  combustion  of 
air  in,  341;  combustion  on  platin- 
ized asbestos,  326;  explosion  with 
air,  326 ;  from  distillation  of  coal 
or  wood,  324,  325;  reciprocal  com- 
bustion of  air  and,  343;  soap-bub- 
bles, 325. 

Ink :  sympathetic,  414. 

Iodic  acid  :  combustion  in  hydrogen, 
346;  decomposition  by  heat,  124; 
reduction  by  carbon  monoxide, 
303 ;  reduction  by  sulphurous  acid, 


125;  from  iodine  and  nitric  acid, 
124. 

Iodic  anhydride:  formation,  124; 
oxidizing  action,  124, 

Iodine :  action  with  ammonia,  206 ; 
action  with  hydrogen  phosphide, 
258 ;  action  with  mercurous  iodide, 
382 ;  action  with  nitric  acid,  124 ; 
action  with  rosin,  119;  action  with 
starch,  114;  distillation,  113;  from 
potassium  iodide,  112;  melting, 
113;  monochloride,123;  solubility, 
114 ;  starch  test  for,  114 ;  trichlo- 
ride, 123;  volatilization,  114; 
union  with  aluminium,  393;  union 
with  hydrogen,  117;  union  with 
mercury,  116,  381 ;  union  with 
phosphorus,  117,  355;  union  with 
potassium,  116;  union  with  zinc 
dust,  116. 

lodo-starch  paper:  action  of  ozone 
on,  35;  preparation,  35;  test  for 
chlorine,  83. 

lodo-starch  solution:  effect  of 
heat  on,  115;  test  for  chlorine, 
83. 

Iron :  absorption  of  oxygen  by  rust- 
ing, 30 ;  action  of  sodium  hydrox- 
ide with  powdered, 42 ;  amalgam, 
381 ;  carbon  in,  411 ;  combustion  in 
carbon  disulphide,  319;  combus- 
tion in  hydrogen  sulphide,  144; 
combustion  in  nitrous  oxide,  211 ; 
combustion  in  oxygen,  24;  com- 
bustion in  sulphur  dioxide,  156; 
combustion  of  gunpowder  and 
powdered,  411;  combustion  of 
potassium  chlorate  and  powdered, 
411 ;  combustion  (quantitative)  in 
air,  27;  deposition  of  copper  on, 
384;  deposition  of  zinc  on,  378; 
explosion  of  oxygen  with  pow- 
dered, 25;  galvanized,  378;  oxide, 
156;  preparation  of  passive,  410; 
preparation  of  pyrophoric,  409; 
union  with  sulphur,  133. 

Jena:  glass,  2. 


430 


INDEX 


Kipp:  generator,  3;  description  of,  46. 

Lead:  action  of  water  on,  401 ;  crys- 
talline structure,  401 ;  deposition 
on  zinc,  401 ;  preparation  of  pyro- 
phoric,400 ;  spontaneous  inflamma- 
bility of  pyrophoric,  400 ;  tree,  401. 

Lead  chromate :  oxidizing  action  of, 
406. 

Lead  dioxide:  union  with  sulphur 
dioxide,  156. 

Lead   monoxide,  219. 

Lead  nitrate:  decomposition  on 
ignition,  219;  explosion  with  sul- 
phur, 403. 

Lead  peroxide,  402. 

Lead  sulphide,  36, 146. 

Lead  tartrate,  400. 

Leidenfrost  phenomenon:  produc- 
tion of,  153. 

Light:  action  on  chlorine  water,  87; 
action  on  cuprous  chloride,  385  ;  ac- 
tion on  green  leaves,  13;  action  on 
potassium  ferricyanide,  412;  ex- 
plosion of  chlorine  and  hydrogen 
by,  90. 

Lime:  chloride  of,  100;  light,  64; 
slaked,  363;  use  in  drying  ammo- 
nia, 192. 

Lithium  carbonate:  reduction  by 
magnesium,  374. 

Magnesite  :  decomposition  by  heat, 
304. 

Magnesium:  action  with  nitric  acid, 
373;  combustion  in  air  (quantita- 
tive), 27;  combustion  in  carbon 
dioxide,  372;  combustion  in  oxy- 
gen, 24;  combustion  in  sulphur 
vapor,  135 ;  combustion  in  water 
vapor,  371 ;  combustion  with  po- 
tassium chlorate,  374;  explosion 
of  chlorine  and  hydrogen  by,  fK); 
reduces  boric  anhydride,  278;  re- 
duces metallic  oxides  and  salts, 
374;  reduces  silicon  dioxide,  283; 
union  with  nitrogen,  375. 

Magnesium     nitride:     action    with 


hydrogen,  376;  decomposition, 
375;  formation,  375. 

Magnesium  silicide:  action  with 
hydrochloric  acid,  284;  formation, 
283,  284. 

Magnesium  sulphide,  135. 

Manganese :  action  of  dioxide  on  hy- 
drochloric acid,  80 ;  action  of  diox- 
ide on  potassium  chlorate,  9,  10; 
silicate,  253;  sulphide,  146. 

Marsh  gas,  319. 

Mercuric  chloride :  action  with  po- 
tassium iodide,  382. 

Mercuric  iodide,  116;  preparation, 
382. 

Mercuric  oxide :  action  with  chlo- 
rine, 98,  99;  oxygen  from,  8; 
ozone  from,  31. 

Mercurous  iodide,  381,  382. 

Mercurous  nitrate  and  ammonia,  194. 

Mercury:  action  of  ozone  on,  36; 
filtration,  381 ;  freezing  with  solid 
carbon  dioxide,  310;  from  mer- 
curic oxide,  8;  precipitation  of 
silver  by,  388;  purification,  381; 
union  with  iodine,  116,  381. 

Metaphosphoric  acid,  267. 

Methane:  explosion  with  oxygen, 
320 ;  non-supporter  of  combustion, 
320;  preparation,  319. 

Mohr's  salt,  213. 

Moisture :  in  bleaching,  87 ;  influ- 
ence on  combustion,  300. 

Mosaic  gold,  399. 

Naphthaline:  action  with  bro- 
mine, 110. 

Newton's  metal,  404. 

Nickel:  deposition  by  electrolysis, 
415;  ignition  of  gunpowder  by 
pyrophoric,  415;  oxidation  in  air, 
415;  pyrophoric,  414;  reduction  of 
oxide,  414;  silicate,  353;  solubil- 
ity of  sulphide  in  sodium  sulphide, 
415;  tetracarbonyl,  416,  418. 

Nitric  acid :  action  with  carbon 
disulphide,  225;  action  with  cop- 
per, 211;    action  with   hydrogen 


INDEX 


431 


sulphide,  144;  action  with  illumi- 
nating gas,  225;  action  with  io- 
dine, 124;  action  with  organic 
matter,  223,  224,  225;  action  with 
tin,  220;  action  witli  turpentine, 
224;  combustion  in  hydrogen, 346; 
combustion  of  illuminating  gas  in, 
225;  decomposition  by  heat,  226; 
dilution  of  fuming,  221 ;  from  po- 
tassium nitrate  and  sulphuric  acid, 
222 ;  test  for,  228. 

Nitric  oxide:  absorption  by  nitric 
acid,  214;  absorption  by  potas- 
sium permanganate  solution,  214; 
action  of  air  on,  215;  combustion 
in,  216;  combustion  of  carbon 
disulphide  in,  217;  combustion  of 
charcoal  in,  217;  from  copper  and 
nitric  acid,  211 ;  from  copper, 
potassium  nitrate,  and  sulphuric 
acid,  212;  from  sodium  nitrite 
and  ferrous  chloride,  212;  neu- 
trality, 213;  reduction  by  hydro- 
gen, 190;  solubility  in  ferrous 
sulphate  solution,  213;  union  with 
oxygen,  215. 

Nitro-benzene :  oxidation  by  lead 
peroxide,  402 ;  oxidation  by  sodium 
peroxide,  351. 

Nitrogen :  from  air,  ammonia,  and 
copper,  183;  from  air  and  burn- 
ing hydrogen,  182;  from  air  and 
phosphorus,  181 ;  from  ammonium 
chloride  and  potassium  dichro- 
mate,  181 ;  from  ammonium  chlo- 
ride and  sodium  nitrite,  180;  from 
ammonium  dichromate,  361;  from 
potassium  nitrate  and  iron,  181; 
oxidation  by  burning  hydrogen, 
185;  oxidation  by  burning  mag- 
nesium, 185;  quantitative  determi- 
nation of,  in  air,  186 ;  volumetric 
relation  in  ammonia,  203. 

Nitrogen  chloride,  204. 

Nitrogen  iodide:  explosiveness  of, 
206;   preparation,  205. 

Nitrogen  peroxide:  absorption  by 
sulphuric  acid,  222;    combustion 


of  charcoal  in,  221 ;  combustion  of 
potassium  in,  221;  decomposition. 
221;  formation  of,  164,  166,  167^ 
215 ;  from  decomposition  of  nitric 
acid,  226;  from  lead  nitrate,  219; 
from  tin  and  nitric  acid,  220; 
vaporization  of  liquid,  220. 

Nitrous  acid :  formation  of,  185, 186 ; 
phenylenediamine  reaction  for, 
218. 

Nitrous  anhydride:  formation  of, 
214,  221 ;  from  arsenic  trioxide  and 
nitric  acid,  218;  liquefaction,  218. 

Nitrous  oxide :  combustion  of  hydro- 
gen in,  210 ;  combustion  of  irou  in, 
211 ;  combustion  of  phosphorus  in, 
210;  combustion  of  splinter  in,  209; 
combustion  of  sulphur  in,  210;  ex- 
plosion with  hydrogen,  210;  from 
ammonium  nitrate,  208;  solubility 
in  water,  209. 

Nordhausen  sulphuric  acid,  160. 

Orthophosphoric  acid,  267. 

Oxygen  :  absorption  by  burning  phos- 
phorus, 21;  absorption  by  potas- 
sium pyrogallate,  26 ;  absorption  by 
rusting  iron,  30;  absorption  from 
air  by  copper  (quantitative) ,  187 ; 
abstraction  from  air  by  phosphorus, 
181 ;  combustion  in  ammonia,  199; 
combustion  in  hydriodic  acid  gas, 
122;  combustion  in  hydrogen,  339- 
341;  combustion  of  candle  in,  18; 
combustion  of  charcoal  in,  18,  19; 
combustion  of  iron  and  magnesium 
powder  in,  24 ;  combustion  of  phos- 
phorus in,  20,  22;  combustion  of 
steel  wool  in,  23;  combustion  of 
sulphur  in,  20,  149;  combustion 
of  wood  in,  17 ;  combustion  of  zinc 
in,  24;  compressed,  14-16;  deter- 
mination of ,  in  air,  186;  explosion 
with  carbon  monoxide,  301 ;  ex- 
plosion with  powdered  aluminium, 
charcoal,  iron,  zinc,  25;  explosion 
with  hydrogen,  69;  from  chloro- 
phyl  of  green  leaves,  13;    from 


432 


INDEX 


electrolysis  of  copper  sulphate, 
13;  from  mercuric  oxide,  8;  from 
potassium  chlorate,  9;  from  potas- 
sium chlorate  and  manganese  di- 
oxide, 10;  from  silver  oxide,  9; 
from  sodium  peroxide,  11 ;  removal 
from  air  by  burning  hydrogen,  182 ; 
separation  by  diffusion,  58;  union 
with  nitric  oxide,  215;  union  with 
sulphur  dioxide,  158. 

Oxyhydrogen  gas :  burner,  64 ;  ex- 
plosion, 70;  flame,  70;  heat  of 
flame,  64,  65;  preparation,  71, 
369. 

Ozone:  action  on  alcohol,  32,  33; 
action  on  ether,  33 ;  action  on  lead 
sulphide,  36;  action  on  mercury, 
36 ;  action  on  phosphorus,  32 ;  action 
on  potassium  iodide,  34,  35 ;  action 
on  rubber,  34 ;  action  on  silver,  33 ; 
action  on  sulphur,  32;  decomposi- 
tion by  copper  oxide,  36;  decom- 
position by  heat,  37 ;  decomposition 
by  rubber,  38;  from  barium  per- 
oxide, 31 ;  from  mercuric  oxide,  31 ; 
from  potassium  chlorate,  31 ;  from 
potassium  permanganate,  32 ;  from 
slow  combustion  of  ether,  34; 
from  slow  oxidation  of  phosphorus, 
3;^;  paper,  preparation,  35. 

Palladium:  precipitation  by  car- 
bon monoxide,  302. 

Paper  wheel,  313. 

Pentathionic  acid,  144. 

Perchloric  acid:  action  on  organic 
matter,  105 ;  bleaching  action,  105 ; 
combustion  of  charcoal  in,  105; 
formation,  104. 

Perchromic  acid,  76. 

Permanganic  anhydride,  32. 

Phosphonium  iodide,  258,  259. 

Phosphpretted  hydrogen :  see  hydro- 
gen phosphide,  249. 

Phosphoric  acid:  formation,  240, 
242,  263. 

Phosphorous  acid:  formation,  261, 
264,  265. 


Phosphorus:  abstraction  of  oxygen 
from  air  by,  181 ;  action  with  bro- 

.  mine,  263;  action  with  chlorine, 
259,  261 ;  action  with  chlorine  mo- 
noxide, 99 ;  action  with  nitric  acid, 
242;  action  with  potassium  chlo- 
rate, 243;  action  with  potassium 
or  sodium  hydroxide,  250;  action 
with  quicklime,  364;  action  with 
sulphur  trioxide,  163;  burns  from. 
233 ;  colors  hydrogen  flame,  241 ; 
combustion  affected  by  charcoal, 
238;  combustion  in  air  (quantita- 
tive), 29,  189;  combustion  in  chlo- 
rine peroxide,  103  ;  combustion  in 
nitric  oxide,  216;  combustion  in 
nitrous  oxide,  210;  combustion  in 
oxygen,  20;  combustion  iu  oxygen 
(quantitative),  22;  combustion  in 
potassium  chlorate,  357 ;  combus- 
tion on  cotton,  239;  combustion 
under  water,  103,  240;  difference 
in  ignition  points  of  modifications, 
247  ;  effect  of  diminished  pressure 
on  glowing,  243 ;  effect  of  oxygen 
on  glowing,  243;  effect  of  vapors 
on  glowing,  244;  inflammability, 
237  ;  oxidation  by  sodium  peroxide, 
351;  precautions  in  handling,  232; 
preparation  of  globules,  236 ;  prep- 
aration of  stick,  235 ;  purification, 
237 ;  red,  see  amorphous ;  reduc- 
tion of  metallic  salt  solutions  by, 
245;  slow  oxidation,  33;  solubility 
in  carbon  disulphide,  238;  test  for 
free,  241;  union  with  iodine,  117; 
vaporization  in  steam,  240. 

Phosphorus,  amorphous :  action  with 
hydrogen,  249;  combustion  in  air, 
248;  combustion  with  potassium 
chlorate,  248 ;  conversion  to  yellow 
by  heat,  246  ;  formation,  240 ;  from 
combustion  of  yellow  phosphorus, 
245 ;  from  action  of  iodine  on  yel- 
low phosphorus,  246 ;  from  action 
of  light  on  yellow  phosphorus,  246. 

Phosphorus  iodide :  action  with 
water,  118. 


INDEX 


433 


Phosphorus  pentachloride,  261. 

Phosphorus  pentoxide :  action  with 
sulphuric  acid,  160;  action  with 
water,  266,  267 ;  from  combustion 
of  phosphorus  in  air  or  oxy- 
gen, 21,  22,  248,  266;  sublimation, 

2m. 

Phosphorus  tribromide,  263. 

Phosphorus  trichloride :  decomposi- 
tion by  water,  260,  265;  prepara- 
tion, 259. 

Plaster  of  Paris,  365. 

Plating:  copper,  384;  nickel,  415; 
silver,  388. 

Platinized  asbestos,  61 ;  action  with 
hydrogen  and  sulphur  dioxide, 
136;  action  with  oxygen  and  sul- 
phur dioxide,  159;  decomposes 
ammonia,  200. 

Platinum:  deflagrating-spoon,  150; 
melting,  65. 

Porous  cell,  55. 

Potable  waters:  action  on  lead 
pipes,  402. 

Potassium :  combustion  in  carbon 
disulphide,  318;  combustion  in 
nitrogen  peroxide,  221 ;  decompo- 
sition of  ammonia  by,  200;  union 
with  bromine,  354;  union  with  io- 
dine, 116,  355;   vaporization,  354. 

Potassium  alum,  395. 

Potassium  chlorate :  action  with  hy- 
drochloric acid,  102;  action  with 
phosphorus,  243;  action  with  sul- 
phuric acid,  102;  combustion  in 
hydrogen,  346  ;  combustion  of 
phosphorus  in,  357 ;  combustion 
with  magnesium,  374;  combustion 
with  powdered  iron,  411 ;  combus- 
tion with  zinc  dust,  378 ;  in  Bengal 
fires,  357;  oxygen  from,  9,  10; 
ozone  from,  31. 

Potassium  cobaltic  nitrite,  414. 

Potassium  dichromate :  action  with 
ammonium  chloride,  181 ;  action 
with  hydrochloric  acid,  82;  action 
with  hydrogen  peroxide,  76;  action 
with  sulphur  dioxide,  154. 


Potassium  disulphate :  decomposi- 
tion, 160. 

Potassium  ferricyanide :  action  of 
light  on,  412. 

Potassium  ferrocyanide :  carbon 
monoxide  from,  29i). 

Potassium  hypophosphite,  250. 

Potassium  iodate :  action  with  chlo- 
rine, 98;  action  with  mercuric 
chloride,  382 ;  action  with  stannous 
chloride,  399 ;  reduction  by  hydra- 
zine sulphate,  229. 

Potassium  nitrate:  in  gunpowder, 
356;  in  touch-paper,  355;  reduc- 
tion by  iron,  181. 

Potassium  perchlorate:  action  with 
sulphuric  acid,  104. 

Potassium  permanganate :  absorp- 
tion of  nitric  oxide  by,  214 ;  ozone 
from,  32 ;  reduction  by  sulphur  di- 
oxide, 156. 

Potassium  pyrogallate :  absorbs  oxy- 
gen, 26,  186;  preparation  of  solu- 
tion, 26. 

Pressure  regulator,  15. 

Pyrophoric:  iron,  409;  lead,  400; 
nickel,  415. 

Realgar,  271. 
Recurved  jet,  85. 
Rose's  metal,  404. 
Rosin :  action  with  iodine,  119. 
Rubber :  action  with  ozone,  38 ;  dif- 
fusion of  hydrogen  through,  57. 

Safety  Lamp,  334. 

Safety  matches,  249. 

Screens:  glass,  5,  102. 

Selenic  acid:  preparation,  179. 

Selenious  acid:  action  with  hydro- 
gen sulphide,  179;  reduction  by 
sulphurous  acid,  179. 

Selenium:  combustion  in  air,  177; 
solubility  in  sulphuric  acid,  177; 
sublimation,  177. 

Selenium  dioxide:  preparation,  178. 

Selenium  sulphide:  formation,  179. 

Silicates :     formation    of    metallic. 


434 


INDEX 


in  solution  of  sodium  silicate, 
352. 

Silicon :  preparation,  283 ;  union 
with  chlorine,  287. 

Silicon  dioxide:  action  with  hydro- 
fluoric acid  gas,  289. 

Silicon  hydride:  combustion  in  air, 
286;  decomposition  by  heat,  286; 
explosion  with  air  or  oxygen,  286; 
spontaneous  combustibility  of, 
285;  preparation,  284. 

Silicon  tetrachloride,  287,  288. 

Silicon  tetrafluoride,  289,  290. 

Silver:  absorption  of  oxygen  by, 
65 ;  action  with  ozone,  33 ;  boiling, 
65;  by  electrolysis,  388;  from 
silver  oxide,  9;  precipitation  by 
carbon  monoxide,  302;  precipita- 
tion by  mercury,  388;  precipita- 
tion by  phosphorus,  245. 

Silver  antimonide,  274. 

Silver  chloride :  absorption  of  am- 
monia, 198. 

Silver  cyanide:  electrolysis  of,  388. 

Silver  iodide :  color  change  on  heat- 
ing, 389 ;  formation,  390. 

Silver  nitrate:  electrolysis  of,  388; 
precipitation  of  silver  from,  388; 
reduction  by  carbon  monoxide, 
302. 

Silver  nitride :  explosiveness  of,  230 ; 
preparation,  230. 

Silver  nitrite,  230. 

Silver  oxide:  action  with  hydrogen 
persulphide,  148 ;  action  with  hy- 
pochlorous  acid,  101;  preparation, 
9;  preparation  of  oxygen  from, 
9;  reduction  by  magnesium,  374,. 

Silver  phosphide:  formation,  241, 
245,  256. 

Slaked  lime,  363. 

Soap-bubbles:  float  on  carbon  diox- 
ide, 313;  hydrogen,  52;  illumi- 
nating gas,  325;  oxyhydrogen,  70; 
solution  for,  52. 

Soda-lime:  absorption  of  carbon 
dioxide  by,  299;  use  in  drying  am- 
monia, 192. 


Soda  water:  carbon  dioxide  in,  306; 
preparation,  316. 

Sodium :  action  on  hydrogen  sul- 
phide, 145;  action  on  water,  40, 
350 ;  manipulation  of,  39 ;  melting, 
349;  metallic  lustre,  349. 

Sodium  acetate:  decomposition, 319. 

Sodium  acid  sulphite :  action  with 
sulphuric  acid,  152. 

Sodium  amalgam:  action  on  alu- 
minium, 391. 

Sodium  chloride :  decomposition  by 
boric  acid,  281. 

Sodium  hypochlorite :  action  on  ar- 
senic, 275;  bleaching  action,  101. 

Sodium  hypophosphite,  266. 

Sodium  peroxide:  action  on  water, 
75 ;  color  change  by  heat,  351 ;  ex- 
plosion with  aluminium,  392;  oxi- 
dizing action  with  carbon,  351; 
oxidizing  action  with  phosphorus, 
351 ;  oxygen  from,  11 ;  preserva- 
tion of,  12. 

Sodium  silicate :  formation  of  me- 
tallic silicates  in,  352. 

Sodium  sulphate :  freezing  mixture 
with  hydrochloric  acid,  352;  su- 
persaturated solution,  351. 

Sodium  sulphide:  formation,  145; 
solubility  of  nickel  sulphide  in, 
415. 

Sparklets,  316. 

Splinters:  cigar-box  wood,  4. 

Spontaneous  combustion :  of  hydro- 
gen phosphide,  251 ;  of  phosphorus, 
238;  of  pyrophoric  iron,  409;  of 
pyrophoric  lead,  400 ;  of  pyrophoric 
nickel.  415 ;  of  silicon  hydride,  284. 

Stannic  chloride,  397,  398. 

Stannic  sulphide,  399. 

Stannous  chloride:  action  with  po- 
tassium iodide,  399;  electrolysis 
of,  396. 

Stannous  iodide,  399. 

Starch:  action  with  iodine,  114, 

Steam  generator,  41,  171. 

Steel  wool :  combustion  in  oxygen, 
23;   rusting  in  air,  30. 


INDEX 


435 


Stibine,  273. 

Stibnite,  139. 

Stroutiuin  nitrate:  deflagration  on 
charcoal,  307;    in  red  fire,  367. 

Suction  pump,  6. 

Sugar:  carbonization  by  sulphuric 
acid,  175;  charring,  291 ;  oxidation 
by  nitric  acid,  225. 

Sulphur:  action  with  sulphuric  acid, 
151 ;  combustion  in  air  or  oxygen, 
149;  combustion  in  nitrous  oxide, 
210;  combustion  in  oxygen,  20; 
deposition  of,  143,  144 ;  distillation 
of,  130 ;  explosion  with  lead  nitrate, 
403 ;  increase  in  weight  on  burning, 
30;  octahedral,  133;  oxidation  by 
nitric  acid,  164;  plastic,  131;  pris- 
matic, 132;  roll,  130;  solubility 
in  carbon  disulphide,  133;  solu- 
bility in  sulphur  monochloride, 
149;  union  with  chlorine,  148; 
union  with  copper,  134 ;  union  with 
hydrogen,  135;  union  with  iron, 
133;  union  with  magnesium,  135; 
union  with  zinc,  135. 

Sulphur  dioxide :  action  with  hydro- 
gen, 136;  action  with  hydrogen 
sulphide,  143;  action  with  nitric 
acid,  164-169;  action  with  potas- 
sium dichromate,  154 ;  action  with 
potassium  permanganate,  156; 
bleaching  action,  155;  combustion 
of  iron  in,  156;  combustion  of  tin 
in,  156;  freezing  action  of,  153; 
from  charcoal  and  sulphuric  acid, 
151 ;  from  copper  and  sulphuric 
acid,  151;  from  sulphur  and  oxy- 
gen, 149;  from  sulphur  trioxide 
and  phosphorus,  163;  from  sul- 
phuric acid  and  sodium  acid  sul- 
phite, 152 ;  from  sulphuric  acid  and 
sulphur,  151 ;  liquefaction  of,  152 ; 
solubility  in  water,  155;  specific 
gravity,  154;  union  with  lead  di- 
oxide, 156 ;  union  with  oxygen ,  158 ; 
volumetric  relation  to  oxygen  con- 
sumed, 150. 

Sulphur  flowers:    action   with  chlo- 


rine monoxide,  99;  combustion 
with  zinc  dust,  378;  deposition, 
142;  in  gunpowder,  356;  prepara- 
tion, 130;  union  with  tin,  399. 

Sulphur  monochloride ;  decomposi- 
tion by  water,  149;  from  chlorine 
and  sulphur,  148;  solubility  of 
sulphur  in,  149. 

Sulphur  sesquioxide,  163. 

Sulphur  trioxide :  action  with  barium 
oxide,  163,  369;  action  with  phos- 
phorus, 163;  action  with  sulphur, 
162 ;  action  with  water,  161 ;  from 
fuming  sulphuric  acid,  160;  from 
oxygen  and  sulphur  dioxide,  158; 
from  potassium  disulphate,  160; 
from  sulphuric  acid  and  phos- 
phorus pentoxide,  160. 

Sulphuretted  hydrogen:  see  hydro- 
gen sulphide,  135. 

Sulphuric  acid :  absorbs  nitrogen 
peroxide,  222 ;  action  on  paper, 
175;  carbonization  of  sugar  by, 
175 ;  dehydrating  action,  174 ;  from 
sulphur  and  nitric  acid,  164;  from 
sulphur  dioxide  and  nitric  acid, 
164-173 ;  heat  of  union  with  water, 
173;  reduction  by  carbon,  151;  re- 
duction by  charcoal,  151;  reduc- 
tion by  copper,  151 ;  reduction  by 
sulphur,  151;  technical  manufac- 
ture, 168. 

Sulphuric  anhydride,  160. 

Sulphurous  acid :  155 ;  action  with 
zinc,  157 ;  electrolysis  of,  157 ;  re- 
duction by  sodium  hypophosphite, 
266. 

Sympathetic  ink,  414. 

Tea  Lead  :  use  of,  40,  253. 

Thermometer :  ether,  174. 

Time  of  reaction,  125. 

Tin:  action  on  nitric  acid, 220;  com- 
bustion in  sulphur  dioxide,  156; 
crystalline  structure,  397 ;  deposi- 
tion by  electrolytic  action,  396; 
deposition  on  zinc,  396;  in  fusible 
alloys,  404 ;    union  with  chlorine, 


436 


INDEX 


397;  union  with  sulphur  flowers, 

399. 
Touch-paper :  preparation,  355. 
Turpentine :    action    with  chlorine, 

86 ;  action  with  nitric  acid ,  224. 

Volumetric  Decomposition  :  of 
ammonia  by  chlorine,  202 ;  of  am- 
monia by  electrolysis,  201 ;  of  am- 
monia by  sodium  hypobromite, 
203 ;  of  hydrochloric  acid  by  elec- 
trolysis, 95-97;  of  water  by  elec- 
trolysis, 71,  72. 

Water:  action  with  sodium,  40, 
350;  electrolysis  of,  71,  72;  from 
combustion  of  hydrogen,  61,  62, 
183 ;  from  cupric  oxide  and  hydro- 
gen, 63. 

Water  blast,  6. 

Water  gas:  preparation,  300. 


Water  vapor:  reduction  by  iron,  41; 
reduction  by  magnesium,  371;  re- 
duction by  zinc,  42. 

Wood:  combustion  in  oxygen,  17;^ 
oxidation  by  chromic  acid,  406. 

Wood's  metal,  404. 

Zinc:  combustion  in  air,  26;  com- 
bustion in  oxygen,  24;'  combustion 
with  potassium  chlorate,  378; 
combustion  with  sulphur,  135; 
combustion  with  sulphur  flowers, 
378;  deposition  of  lead  on,  401; 
deposition  on  iron,  378;  explosion 
with  oxygen,  25;  granulated,  377  ; 
ignition  by  ammonium  nitrate, 
361;  union  with  iodine,  116;  use 
in  galvanizing,  378. 

Zinc  oxide :  formation,  26. 

Zinc  sulphide:  formation,  135,  146, 
378. 


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With  explanatory  notes  and  stoichiometrical  problems,  by  Henry  P.  Talbot, 
Ph.D.,  Professor  of  Analytical  Chemistry  in  the  Massachusetts  Institute 
of  Technology.     Third  edition,  revised  and  enlarged. 

8vo  Cloth  $  J^O 

The  Spirit  of  Organic  Chemistry 

An  introduction  to  the  current  literature  of  the  subject  by  Arthur  Lach- 
MAN,  Professor  of  Chemistry  in  the  University  of  Oregon.. 

Cloth  J2mo  $  J^O 

Lessons  in  Elementary  Chemistry 

By  Sir  Henry  Roscoe,  F.R.S. 
Cloth  J2mo  $  L25 


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